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    My Journey through the Astronomical Year

    Think of this as a "companion text" to this, the main web site. Not required reading, butI hope you'll find it interesting and helpful.

Look North: May is the month the North Star gets two bright flankers!

Click for larger image. (Developed from Starry Nights Pro screen shot.)

Click here to download a printer-friendly version of this chart.

Is the North Star – Polaris – our brightest star? No! And it certainly won’t look that way this month as it shares the northern sky with two very bright stars. But, read on. Polaris is not nearly as dim as it looks!

If you have been learning your guidepost stars as they rise in the East, you won’t be surprised by the two bright stars which flank – and outshine – our pole star in May. To the northwest is Capella, a star we first met when it rose in the northeast in November. In May the northeast is dominated by a star that is almost Capella’s twin in brightness, Vega, a guidepost star we introduce in May. (See “Look East!” for more about Vega.) As a bonus we also have the twin guidepost stars, Castor and Pollux, making their way into the northern sky high above Capella. But let’s focus on Capella and Vega.

New star watchers frequently assume the North Star, Polaris, will be the brightest star in the sky. It isn’t even close! It is bright, but its fame comes because it’s very, very close to where the axis of the Earth points to the north celestial pole. So it serves anyone trying to find true north as a very good guide. But when it comes to brightness, it’s in the same league as the stars in the Big Dipper. Quite bright, but it can’t hold a candle to Capella and Vega. When you look at a list of the brightest stars, Vega is number 5 and Capella number 6. Polaris, our North Star, is number 48!

As simple as one, two, three!

That doesn’t mean Polaris is a slouch, though. First, in the eastern sky in May you meet Spica. (That’s on our chart for the east.) One distinction of Spica is that it’s as close to being magnitude 1 as any star gets. A distinction of Polaris is, as Spica defines magnitude 1, Polaris defines magnitude 2. (To be precise it’s magnitude 2.02.) Vega and Capella are extremely close to magnitude 0. Vega is 0.03 and Capella 0.08. Good luck on telling the difference! This month, if you look north 90 minutes after sunset, you may think Capella is a bit brighter actually – but if it appears that way it will be because it’s a bit higher in the sky and thus is not dimmed by having to fight its way through as much of our atmosphere as Vega is doing at the moment. So don’t try to split hairs. And yes, you’re right – they are NOT really as “simple as one, two, three” – on the magnitude scale they are as simple as zero, one, two – but that doesn’t sound as good! (Vega and Capella are zero; Spica is magnitude one, and Polaris, magnitude two.)

So which is really the brightest star of these four? Are you ready for this? Polaris! That’s right – if you put all four stars at the same distance, Polaris would appear to be the brightest. Remember, that the lower the magnitude number, the brighter the star. In absolute magnitude – the brightness we give to a star if they are all shining from the same distance  – these four stars line up this way:

  • Polaris -3.4
  • Spica -3.2
  • Capella 0.1
  • Vega 0.3

And those absolute magnitudes also reflect their order in distance from us.

  • Polaris 433 light years
  • Spica 250 light years
  • Capella 45 light years
  • Vega 25 light years

So sometimes a star is very bright because it’s – well, very bright. But sometimes it only appears to be very bright because it is very close to us. If you put our closest star into this group, our Sun – remember, it is just 8 light minutes from us – in absolute magnitude it would be by far the dimmest of this group – absolute magnitude 4.9! So while Polaris doesn’t look all that bright, it really is a very bright star! Another way to think about this is if you move our Sun out to where Polaris is, it would be about magnitude 10! You would need binoculars or a telescope to see it!

Click image for larger view of this chart. Yellow circle represents typical field of view for low power binoculars, such as 10X50.

To get an idea of the difference between Polaris and our Sun, point your binoculars towards Polaris.  You should be able to make out the “Engagement Ring” asterism – granted, a crude ring with Polaris as the diamond.  This asterism points you towards the true north celestial pole  – just avery short distance to the other side of Polaris –  and also gives you a good idea of about how far Polaris is from that pole.  Small binoculars will not show you the companion of Polaris, but to get an idea of how bright our Sun would be at the same distance, look for the star labelled 9.8 – and if you can’t see it, see if you can see the star that’s a bit brighter labelled “9.”  Don’t expect to see these instantly. Sit calmly, relax, and keep looking for at least a minute.

And here’s one more cool secret about Polaris. It has a companion that just happens to be quite dim – magnitude 9. It’s fun to see the two of them if you have a small telescope, though it’s not all that easy because Polaris is so much brighter than its companion. But if you get a chance to see Polaris and its companion in a telescope, remind yourself that the very faint companion is still a bit brighter than our Sun would look at this distance. This companion, known as Polaris B, was discovered in 1780 by William Herschel, and for many years Polaris was thought to be a binary star – that is, a system of two stars orbiting about a common center of gravity. But Polaris was holding one more surprise – it’s really a triple star.

The top image shows Polaris and its faint companion that can be seen in any decent backyard telescope. The bottom image shows the second companion, Polaris Ab, which has only been seen by using the Hubble Space Telescope.

This has been known for some time, but no one could see the third star until they turned the Hubble Space telescope on it in 2006. That’s when NASA released the first image of this third companion. The accompanying press release explained it this way:

By stretching the capabilities of NASA’s Hubble Space Telescope to the limit, astronomers have photographed the close companion of Polaris for the first time. They presented their findings  in a press conference at the 207th meeting of the American Astronomical Society in Washington, D.C.

“The star we observed is so close to Polaris that we needed every available bit of Hubble’s resolution to see it,” said Smithsonian astronomer Nancy Evans (Harvard-Smithsonian Center for Astrophysics). The companion proved to be less than two-tenths of an arc second from Polaris — an incredibly tiny angle equivalent to the apparent diameter of a quarter located 19 miles away. At the system’s distance of 430 light years, that translates into a separation of about 2 billion miles.

“The brightness difference between the two stars made it even more difficult to resolve them,” stated Howard Bond of the Space Telescope Science Institute (STScI). Polaris is a supergiant more than two thousand times brighter than the Sun, while its companion is a main-sequence star. “With Hubble, we’ve pulled the North Star’s companion out of the shadows and into the spotlight.”

So as I said, Polaris is no slouch. It not only is a very bright star, but it also has two companions, and scientists are still studying it because it is unusual in other respects. We’ll talk about those other differences another month.

Look East! Drive a Spike to Spica (pronounced Spy-ka) and two planets in May 2014!

If you followed “the arc” of the Big Dipper ‘s handle last month to find Arcturus, then you “drive a spike”  this month to find Spica –  pronounced Spy-ka – plus Mars and Saturn. It’s like taking a long, cool slide from the Dipper – and the “Arc-to-Arcturus” and “Spike-to-Spica” relationships hold true as long as these stars are in our skies – which will be right through August.

Here’s how it looks – remember: look east  starting about an hour after Sunset.  Arcturus, Spica, and Mars should all be visible as the first stars emerge, but Saturn will have to wait a bit. At the start of the month it may be too low until about two hours after sunset – but each night it rises earlier and earlier. On May 10 it is in opposition, rising as the sun sets.

Click to enlarge. (Prepared from Starry Nights Pro screen shot.)

Click to enlarge. (Prepared from Starry Nights Pro screen shot.)

Click here to download a printer-friendly version of this chart.

While the Dipper is easy to recognize, its stars are second magnitude – bright, but easily out-shone by the triangle of Arcturus, Mars, and Saturn. Even Spica, almost exactly magnitude 1, is brighter than the Dipper stars. Still, the Dipper stars will be very high in the northeast and easy to spot as it gets dark.  The brightest star in this section of the sky is Arcturus at magnitude minus 0.04. (Remember, the lower the magnitude number, the brighter the object – minus magnitude are brighter still.) The next brightest star you’ll see is over to your left, low in the northeast – Vega at magnitude 0.04. So Vega is barely on the plus side of  magnitude  zero and Arcturus is barely on the minus side, a difference that is next to impossible to detect with the eye. This year both these stars will be out shone by Mars, almost magnitude -1,  and Saturn is just a tad dimmer than Arcturus and Vega, though about a full magnitude dimmer than Mars.  Together these  five –  Mars, Arcturus, Vega, Saturn, and Spica will give you a good sense of the magnitude scale. In fact, throw in Polaris – the North Star, which is almost exactly magnitude 2 and you have a range of four magnitudes represented – quite a brilliant display.

The color contrast is exceptional here too. As these stars and planets get higher in the sky, you will notice that Mars is definitely reddish, Spica is a rich blue, while Saturn has a yellow tint.

We dealt with Arcturus last month. Saturn will be in our sky all night and as always is a treat for the small telescope user. From a naked eye perspective,  it’s fun to remember that the name “planet” means “wanderer” in Greek, but all “wanderers” are not created equal. Mars, Venus, and Mercury move  so quickly in our night sky that you can easily mark their changes over a period of a few days -certainly a week.  Saturn is much more sluggish.

Saturn changes position over the course of an entire year by roughly 12 degrees.  To see this in the sky , find Saturn. Hold your fist at arms length so Saturn is just below it. Just above your fist is where Saturn was last year. Put Saturn on top of your fist and just below your fist is where it will be next year. So how long will it take Saturn to get around the sky to roughly the same position? Well, 360/12 = about 30 years!  Now if you think a moment, the Moon takes about 30 days to get around our sky – and that means the Moon moves each day about 12  degrees –  the same apparent distance covered by Saturn each year.  All of which should tell you that it would be reasonable to assume Saturn is much farther away from us than the Moon – which, of course, it is.

None of this is rocket science, but I find it interesting to contemplate as I look up and see Saturn. I measure that distance it will travel in the next year and in my mind’s eye I stand above the Solar System and I see a long thin pie slice reaching from me to Saturn’s distance orbit and this helps me keep things in perspective – gives me a better intuitive feel for the neighborhood in which we live.  OK – for the record Saturn is moving at about 22,000 miles an hour, Mars about 54,000 miles an hour in a much shorter orbit, and we’re whipping right along close to 67,000 miles an hour – and we don’t even feel the wind in our face! Oh – and Saturn’s actual orbital period is 29.458 years.

On to this month’s new guidepost stars!

Vega and Spica are each fascinating stars, but let’s start with Vega. Shining brightly not far above the northeastern horizon as the evening begins, Vega comes about as close to defining the word “star” as you can get. In “The Hundred Greatest Stars” James Kaler calls it “the ultimate standard star” because its magnitude is about as close to zero as you can get  and its color is about as close to white as you can get. (If you’re one of those who assumed all stars are white, you’re forgiven. Individuals vary in their ability to see different colors in stars and for everyone the color differences are subtle – in fact I think of them as tints rather than colors. )

It’s hard not to be attracted to Vega when you read Leslie Peltier’s wonderful autobiography, “Starlight Nights.” Vega was central to his astronomical observing throughout his career because he began with it when he first started reading the book from which I got the idea for this web site, “The Friendly Stars” by Martha Evans Martin. Peltier wrote:

According to the descriptive text Vega, at that very hour in the month of May, would be rising in the northeastern sky. I took the open book outside, walked around to the east side of the house, glanced once more at the diagram by the light that came through the east window of the kitchen, looked up towards the northeast and there, just above the plum tree blooming by the well, was Vega. And there she had been all the springtimes of my life, circling around the pole with her five attendant stars, fairly begging for attention, and I had never seen her.

Now I knew a star! It had been incredibly simple, and all the stars to follow were equally easy.

Vega went on to be the first target of the 2-inch telescope he bought with the $18 he made by raising and picking strawberries. (This was around 1915.) And Vega became the first target for every new telescope he owned until his death in 1980. If you still don’t know a star, go out and introduce yourself to Vega early on a May evening. Even without a plum tree to look over, you can’t miss her! And once you’ve done that you’re well on your way to making the night sky your own.  (And yes, Vega is the star from which the message comes in Carl Sagan’s book/movie “Contact.”)

Vital stats for Vega, also known as Alpha Lyrae:

• Brilliance: Magnitude .03 ; a standard among stars; total radiation is that of 54 Suns.
• Distance: 25 light years
• Spectral Type: A0 Dwarf
• Position: 18h:36m:56s, +38°:47′:01″

Spica, a really bright star – honest!

Spica is truly a very bright star, but the numbers you may read for its brightness can have you pulling your hair. That’s because there are at least four common ways to express the brightness of Spica and other stars, and writers don’t always tell you which way they’re using. So let’s look at these four ways and see what they mean for Spica.

The first is the most obvious. How bright does it look to you and me from our vantage point on Earth using our eyes alone? We then assign it a brightness using the magnitude system with the lower the number, the brighter star. (For full discussion of this system, see “How bright is that star?”)

By this measure Spica is 16th on the list of brightest stars and is about as close as you can come to being exactly magnitude 1. (Officially 1.04) Though I should add here that the number really marks the midpoint of a magnitude designation – that is, any star that is in the range of magnitude .5 to magnitude 1.5 is called “magnitude 1” and so on for the other numbers on the scale.

But that scale talks about what we see. It doesn’t account for distance. Obviously if you have two 60-watt light bulbs and one is shining 6 feet away from you and the other 1,000 feet away, they are not going to look the same brightness. But if we put them both at the same distance – say 100 feet – they would look the same. So it is with stars. To compare them we pretend they all were at the same distance – in this case 10 parsecs, which is about 32.6 light years. Put our Sun at that distance and it would be magnitude 4.83. (That’s about as faint as the fainest stars we see in the Little Dipper.) We call that its absolute magnitude.

The absolute magnitude for Spica is -3.55 – not quite as bright as dazzling Venus.

Wow! That’s pretty bright compared to our Sun! Yes it is. Sun 4.83; Spica -3.55. Don’t miss the “minus” sign in front of Spica’s number! That means there’s more than eight magnitudes difference between the Sun and Spica. And that relates to the next figure you are likely to see quoted. Something that is called its luminosity. Luminosity compares the brightness of a star to the brightness of our Sun. Unfortunately, the term is often misused – or poorly defined. Thus in the Wikipedia article I just read on Spica it said that “Spica has a luminosity about 2,300 times that of the Sun.” Yes, but what does that mean? It means that if we were to put the two side by side, Spica would appear to our eyes to be 2,300 times as bright as our Sun.

That is bright! But there’s more, much more. Spica is also a very hot star – in fact one of the brightest hot stars that we see with our naked eyes. But we miss most of that brightness because most of it is being radiated in forms of energy that our eyes don’t detect. In the case of Spica, that is largely ultraviolet energy. The Wikipedia article actually listed Spica’s luminosity twice, and the second time it gave it as “13,400/1,700.”

Oh boy – now we have Spica not 2,300 times as bright as the Sun, but more than 13,000 times as bright. Now that IS bright – but is it right? Yes! So why the difference? Again, the first “luminosity” given – 2,300 times that of the Sun – is measuring only what we can see with our eyes. The second is measuring total amount of electromagnetic radiation a star radiates and is properly called the “bolometric luminosity.” And why two numbers for that last figure? 13,400/1,700? Because while Spica looks like one star to us, it is really two stars that are very close together and one is much brighter than the other. So what we see as one star is really putting out energy in the neighborhood of 15,100 times as much as our Sun.

This can get confusing, so I suggest you remember three things about Spica.

1. It defines first magnitude, having a brightness as it appears to us of 1.04.

2. It is really far brighter (magnitude -3.55), but appears dim because it is far away – about 250 light years by the most recent measurements.

3. It is very hot – appearing blue to our eyes – and because it is very hot it is actually radiating a lot more energy in wavelengths we don’t see, so it is far, far brighter than our Sun.

Spica is the brightest star in the constellation Virgo, one of those constellations where you can not really connect the dots and form a picture of a virgin unless you have an over abundance of imagination. Besides, the remaining stars are relatively faint. That’s why we focus on the bright stars and sometimes those simple patterns known as “asterisms” and use them as our guides.

Vital stats for Spica, also known as Alpha Virgo:

• Brilliance: Magnitude 1.04; a close double whose combined radiation is the equal of 15,100 Suns.
• Distance: 250 light years
• Spectral Types: B1,B4 Dwarfs
• Position: 13h:25m:12s, -11°:09′:41″

Guideposts reminder

Each month you’re encouraged to learn the new “guidepost” stars rising in the east about an hour after sunset. One reason for doing this is so you can then see how they move in the following months. If you have been reading these posts for several months, you may want to relate Spica to two earlier guidepost stars with which it forms a right triangle, Arcturus and Regulus.

Once you have identified the Right Triangle, note carefully the positions of Spica and Regulus. They pretty much mark the “ecliptic.” This is the path followed by the Sun. Also, within a few degrees north or south of it, you will find the planets and the Moon. That’s well illustrated in 2014 by the presence of both Saturn and Mars, very near the ecliptic, as noted on our chart.

Arcturus and Regulus are not the only guidepost stars and asterisms in the May sky. Again, if you have been reading these posts for several months, be sure to find the stars and asterisms you found in earlier months. Early on a May evening these will include, from east to west, the following: Arcturus, Spica, Saturn, Leo’s Rump (triangle), The Sickle,  Mars, Regulus, the Beehive, Procyon, Sirius, Pollux, Castor, and in the northwest near the horizon, Capella, and the Kite. Venus will be a bright evening “star” in the west, and if you look early in the month you may catch a glimpse of Sirius and Betelgeuse before they set.

Look East! Drop off the slide to Spica and land on Saturn in May 2013!

If you followed “the arc” of the Big Dipper ‘s handle last month to find Arcturus, then you can do the same this month to find Spica – it’s like taking a long, cool slide from the Dipper – and if you hop off just before just before the end, this year you’ll land on Saturn!

Here’s how it looks – remember: look east  starting about an hour after Sunset.  But don’t wait too long – as the night goes on, everything will appear to rise and after a few hours this chart won’t be much help.

stuff

Start with the Big Dipper, high overhead tot he east. Following the arc of its handle, slide down to the brightest star int he east, Arcturus. Soften your slide and keep going and you’ll come to another bright star, Spica. Hopwever, if you hop off the slide just before getting to Spica, you’ll land on Saturn – which will be brighter than Spica, but not quite as bright as Arcturus.

Click here to download a printer-friendly version of this chart.

While the Dipper is easy to recognize, its stars are second magnitude – bright, but not the brightest. The brightest star in this section of the sky is Arcturus at magnitude zero. (Remember, the lower the magnitude number, the brighter the object.) The next brightest star you’ll see is over to your left, low in the northeast – Vega. In fact, Vega is magnitude  zero as well and the difference between it an Arcturus is next to impossible to detect with the eye. And this year we can say the same about Saturn  – it is over near  Spica and will outshine it by just a tad and be nearly as bright as Vega and Arcturus. All of these – Arcturus, Vega, Saturn, and Spica will be brighter than any of the Dipper stars.

As these stars get higher in the sky, you will notice that Spica is a rich blue, while Saturn has a yellow tint. About an hour after sunset Vega will be the lowest at about 20-degrees above the horizon – two fists held at arms length. Saturn will be about 23 degrees above the horizon, Spica about 30 degrees, Arcturus 47 degrees and Alkaid, the star at the end of the big Dipper’s handle, about 64 degrees.

We dealt with Arcturus last month. Saturn will be in our sky most of the night and as always is a treat for the small telescope user. From a naked eye perspective,  it’s fun to remember that the name “planet” means “wanderer” in Greek, but all “wanderers” are not created equal. Mars, Venus, and Mercury move  so quickly in our night sky that you can easily mark their changes over a period of a few days -certainly a week.  Saturn is much more sluggish.

Look at the chart and you’ll see how little Saturn changes position over the course of an entire year – it moves roughly 12 degrees.  To see this in the sky , find Saturn. Hold your fist at arms length so Saturn is just below it. Just above your fist is where Saturn was last year. Put Staurn on top of your fist and just below your fist is where it will be next year. So how long will it take Saturn to get around the sky to roughly the same position? Well, 360/12 = about 30 years!  Now if you think a moment, the Moon takes about 30 days to get around our sky – and that means the Moon moves each day about 12  degrees –  the same apparent distance covered by Saturn each year.  All of which should tell you that it would be reasonable to assume Saturn is much farther away from us than the Moon – which, of course, it is.

None of this is rocket science or in any way  profound, but I find it interesting to contemplate as I look up and see Saturn. I measure that distance it will travel in the next year and in my mind’s eye I perch above the Solar System and I see a long thin pie slice reaching from me to Saturn’s distance orbit and this helps me keep things in perspective – gives me a better intuitive feel for the neighborhood in which we live.  OK – for the record Saturn is moving at about 22,000 miles an hour, Mars about 54,000 miles an hour in a much shorter orbit, and we’re whipping right along close to 67,000 miles an hour – and we don’t even feel the wind in our face! Oh – and Saturn’s actual orbital period is 29.458 years.

On to this month’s new guidepost stars!

Vega and Spica are each fascinating stars, but let’s start with Vega. Shining brightly not far above the northeastern horizon as the evening begins, Vega comes about as close to defining the word “star” as you can get. In “The Hundred Greatest Stars” James Kaler calls it “the ultimate standard star” because its magnitude is about as close to zero as you can get (.03) and its color is about as close to white as you can get. (If you’re one of those who assumed all stars are white, you’re forgiven. Individuals vary in their ability to see different colors in stars and for everyone the color differences are subtle – in fact I think of them as tints rather than colors. )

It’s hard not to be attracted to Vega when you read Leslie Peltier’s wonderful autobiography, “Starlight Nights.” Vega was central to his astronomical observing throughout his career because he began with it when he first started reading the book from which I got the idea for this web site, “The Friendly Stars” by Martha Evans Martin. Peltier wrote:

According to the descriptive text Vega, at that very hour in the month of May, would be rising in the northeastern sky. I took the open book outside, walked around to the east side of the house, glanced once more at the diagram by the light that came through the east window of the kitchen, looked up towards the northeast and there, just above the plum tree blooming by the well, was Vega. And there she had been all the springtimes of my life, circling around the pole with her five attendant stars, fairly begging for attention, and I had never seen her.

Now I knew a star! It had been incredibly simple, and all the stars to follow were equally easy.

Vega went on to be the first target of the 2-inch telescope he bought with the $18 he made by raising and picking strawberries. (This was around 1915.) And Vega became the first target for every new telescope he owned until his death in 1980. If you still don’t know a star, go out and introduce yourself to Vega early on a May evening. Even without a plum tree to look over, you can’t miss her! And once you’ve done that you’re well on your way to making the night sky your own.  (And yes, Vega is the star from which the message comes in Carl Sagan’s book/movie “Contact.”)

Vital stats for Vega, also known as Alpha Lyrae:

• Brilliance: Magnitude .03 ; a standard among stars; total radiation is that of 54 Suns.
• Distance: 25 light years
• Spectral Type: A0 Dwarf
• Position: 18h:36m:56s, +38°:47′:01″

Spica, a really bright star – honest!

Spica is truly a very bright star, but the numbers you may read for its brightness can have you pulling your hair. That’s because there are at least four common ways to express the brightness of Spica and other stars, and writers don’t always tell you which way they’re using. So let’s look at these four ways and see what they mean for Spica.

The first is the most obvious. How bright does it look to you and me from our vantage point on Earth using our eyes alone? We then assign it a brightness using the magnitude system with the lower the number, the brighter star. (For full discussion of this system, see “How bright is that star?”)

By this measure Spica is 16th on the list of brightest stars and is about as close as you can come to being exactly magnitude 1. (Officially 1.04) Though I should add here that the number really marks the midpoint of a magnitude designation – that is, any star that is in the range of magnitude .5 to magnitude 1.5 is called “magnitude 1” and so on for the other numbers on the scale.

But that scale talks about what we see. It doesn’t account for distance. Obviously if you have two 60-watt light bulbs and one is shining 6 feet away from you and the other 1,000 feet away, they are not going to look the same brightness. But if we put them both at the same distance – say 100 feet – they would look the same. So it is with stars. To compare them we pretend they all were at the same distance – in this case 10 parsecs, which is about 32.6 light years. Put our Sun at that distance and it would be magnitude 4.83. (That’s about as faint as the fainest stars we see in the Little Dipper.) We call that its absolute magnitude.

The absolute magnitude for Spica is -3.55 – not quite as bright as dazzling Venus.

Wow! That’s pretty bright compared to our Sun! Yes it is. Sun 4.83; Spica -3.55. Don’t miss the “minus” sign in front of Spica’s number! That means there’s more than eight magnitudes difference between the Sun and Spica. And that relates to the next figure you are likely to see quoted. Something that is called its luminosity. Luminosity compares the brightness of a star to the brightness of our Sun. Unfortunately, the term is often misused – or poorly defined. Thus in the Wikipedia article I just read on Spica it said that “Spica has a luminosity about 2,300 times that of the Sun.” Yes, but what does that mean? It means that if we were to put the two side by side, Spica would appear to our eyes to be 2,300 times as bright as our Sun.

That is bright! But there’s more, much more. Spica is also a very hot star – in fact one of the brightest hot stars that we see with our naked eyes. But we miss most of that brightness because most of it is being radiated in forms of energy that our eyes don’t detect. In the case of Spica, that is largely ultraviolet energy. The Wikipedia article actually listed Spica’s luminosity twice, and the second time it gave it as “13,400/1,700.”

Oh boy – now we have Spica not 2,300 times as bright as the Sun, but more than 13,000 times as bright. Now that IS bright – but is it right? Yes! So why the difference? Again, the first “luminosity” given – 2,300 times that of the Sun – is measuring only what we can see with our eyes. The second is measuring total amount of electromagnetic radiation a star radiates and is properly called the “bolometric luminosity.” And why two numbers for that last figure? 13,400/1,700? Because while Spica looks like one star to us, it is really two stars that are very close together and one is much brighter than the other. So what we see as one star is really putting out energy in the neighborhood of 15,100 times as much as our Sun.

This can get confusing, so I suggest you remember three things about Spica.

1. It defines first magnitude, having a brightness as it appears to us of 0.98 – closer than any other star to magnitude 1.

2. It is really far brighter (magnitude -3.55), but appears dim because it is far away – about 250 light years by the most recent measurements.

3. It is very hot – appearing blue to our eyes – and because it is very hot it is actually radiating a lot more energy in wavelengths we don’t see, so it is far, far brighter than our Sun.

Spica is the brightest star in the constellation Virgo, one of those constellations where you can not really connect the dots and form a picture of a virgin unless you have an over abundance of imagination. Besides, the remaining stars are relatively faint. That’s why we focus on the bright stars and sometimes those simple patterns known as “asterisms” and use them as our guides.

Vital stats for Spica, also known as Alpha Virgo:

• Brilliance: Magnitude .98 ; as close to magnitude 1 as any star gets; a close double whose combined radiation is the equal of 15,100 Suns.
• Distance: 250 light years
• Spectral Types: B1,B4 Dwarfs
• Position: 13h:25m:12s, -11°:09′:41″

Guideposts reminder

Each month you’re encouraged to learn the new “guidepost” stars rising in the east about an hour after sunset. One reason for doing this is so you can then see how they move in the following months. If you have been reading these posts for several months, you may want to relate Spica to two earlier guidepost stars with which it forms a right triangle, Arcturus and Regulus. Here’s what that triangle looks like.

Click image for larger view. (Created, with modifications, from Starry Nights Pro screen shot.)

Click here to download a printer-friendly version of this chart.

Once you have identified the Right Triangle, note carefully the positions of Spica and Regulus. They pretty much mark the “ecliptic.” This is the path followed by the Sun. Also, within about 9 degrees north or south of it, you will find the planets and the Moon. That’s well illustrated in 2012 by the presence of both Saturn and Mars, very near the ecliptic, as noted on our chart.

Arcturus and Regulus are not the only guidepost stars and asterisms in the May sky. Again, if you have been reading these posts for several months, be sure to find the stars and asterisms you found in earlier months. Early on a May evening these will include, from east to west, the following: Arcturus, Spica, Saturn, Leo’s Rump (triangle), The Sickle,  Mars, Regulus, the Beehive, Procyon, Sirius, Pollux, Castor, and in the northwest near the horizon, Capella, and the Kite. Venus will be a bright evening “star” in the west, and if you look early in the month you may catch a glimpse of Sirius and Betelgeuse before they set.

Look North: May is the month Polaris ( the North Star) gets two bright flankers!

Click for larger image. (Developed from Starry Nights Pro screen shot.)

Click here to download a printer-friendly version of this chart.

Is the North Star – Polaris – our brightest star? No! And it certainly won’t look that way this month as it shares the northern sky with two very bright stars. But, read on. Polaris is not nearly as dim as it looks!

If you have been learning your guidepost stars as they rise in the East, you won’t be surprised by the two bright stars which flank – and outshine – our pole star in May. To the northwest is Capella, a star we first met when it rose in the northeast in November. In May the northeast is dominated by a star that is almost Capella’s twin in brightness, Vega, a guidepost star we introduce in May. (See “Look East!” for more about Vega.) As a bonus we also have the twin guidepost stars, Castor and Pollux, making their way into the northern sky high above Capella. But let’s focus on Capella and Vega.

New star watchers frequently assume the North Star, Polaris, will be the brightest star in the sky. It isn’t even close! It is bright, but its fame comes because it’s very, very close to where the axis of the Earth points to the north celestial pole. So it serves anyone trying to find true north as a very good guide. But when it comes to brightness, it’s in the same league as the stars in the Big Dipper. Quite bright, but it can’t hold a candle to Capella and Vega. When you look at a list of the brightest stars, Vega is number 5 and Capella number 6. Polaris, our North Star, is number 48!

As simple as one, two, three!

That doesn’t mean Polaris is a slouch, though. First, in the eastern sky in May you meet Spica. (That’s on our chart for the east.) One distinction of Spica is that it’s as close to being magnitude 1 as any star gets. A distinction of Polaris is, as Spica defines magnitude 1, Polaris defines magnitude 2. (To be precise it’s magnitude 2.02.) Vega and Capella are extremely close to magnitude 0. Vega is 0.03 and Capella 0.08. Good luck on telling the difference! This month, if you look north 90 minutes after sunset, you may think Capella is a bit brighter actually – but if it appears that way it will be because it’s a bit higher in the sky and thus is not dimmed by having to fight its way through as much of our atmosphere as Vega is doing at the moment. So don’t try to split hairs. And yes, you’re right – they are NOT really as “simple as one, two, three” – on the magnitude scale they are as simple as zero, one, two – but that doesn’t sound as good! (Vega and Capella are zero; Spica is magnitude one, and Polaris, magnitude two.)

So which is really the brightest star of these four? Are you ready for this? Polaris! That’s right – if you put all four stars at the same distance, Polaris would appear to be the brightest. Remember, that the lower the magnitude number, the brighter the star. In absolute magnitude – the brightness we give to a star if they are all shining fromt he same distance  -these four stars line up this way:

  • Polaris -3.4
  • Spica -3.2
  • Capella 0.1
  • Vega 0.3

And those absolute magnitudes also reflect their order in distance from us.

  • Polaris 433 light years
  • Spica 250 light years
  • Capella 45 light years
  • Vega 25 light years

So sometimes a star is very bright because it’s – well, very bright. But sometimes it only appears to be very bright because it is very close to us. If you put our closest star into this group, our Sun – remember, it is just 8 light minutes from us – in absolute magnitude it would be by far the dimmest of this group – absolute magnitude 4.9! So while Polaris doesn’t look all that bright, it really is a very bright star! Another way to think about this is if you move our Sun out to where Polaris is, it would be about magnitude 10! You would need binoculars or a telescope to see it!

Click image for larger view of this chart. Yellow circle represents typical field of view for low power binoculars, such as 10X50.

To get an idea of the difference between Polaris and our Sun, point your binoculars towards Polaris.  You should be able to make out the “Engagement Ring” asterism – granted, a crude ring with Polaris as the diamond.  This asterism points you towards the true north celestial pole  – just avery short distance to the other side of Polaris –  and also gives you a good idea of about how far Polaris is from that pole.  Small binoculars will not show you the companion of Polaris, but to get an idea of how bright our Sun would be at the same distance, look for the star labelled 9.8 – and if you can’t see it, see if you can see the star that’s a bit brighter labelled “9.”  Don’t expect to see these instantly. Sit calmly, relax, and keep looking for at least a minute.

And here’s one more cool secret about Polaris. It has a companion that just happens to be quite dim – magnitude 9. It’s fun to see the two of them if you have a small telescope, though it’s not all that easy because Polaris is so much brighter than its companion. But if you get a chance to see Polaris and its companion in a telescope, remind yourself that the very faint companion is still a bit brighter than our Sun would look at this distance. This companion, known as Polaris B, was discovered in 1780 by William Herschel, and for many years Polaris was thought to be a binary star – that is, a system of two stars orbiting about a common center of gravity. But Polaris was holding one more surprise – it’s really a triple star.

The top image shows Polaris and its faint companion that can be seen in any decent backyard telescope. The bottom image shows the second companion, Polaris Ab, which has only been seen by using the Hubble Space Telescope.

This has been known for some time, but no one could see the third star until they turned the Hubble Space telescope on it in 2006. That’s when NASA released the first image of this third companion. The accompanying press release explained it this way:

By stretching the capabilities of NASA’s Hubble Space Telescope to the limit, astronomers have photographed the close companion of Polaris for the first time. They presented their findings  in a press conference at the 207th meeting of the American Astronomical Society in Washington, D.C.

“The star we observed is so close to Polaris that we needed every available bit of Hubble’s resolution to see it,” said Smithsonian astronomer Nancy Evans (Harvard-Smithsonian Center for Astrophysics). The companion proved to be less than two-tenths of an arc second from Polaris — an incredibly tiny angle equivalent to the apparent diameter of a quarter located 19 miles away. At the system’s distance of 430 light years, that translates into a separation of about 2 billion miles.

“The brightness difference between the two stars made it even more difficult to resolve them,” stated Howard Bond of the Space Telescope Science Institute (STScI). Polaris is a supergiant more than two thousand times brighter than the Sun, while its companion is a main-sequence star. “With Hubble, we’ve pulled the North Star’s companion out of the shadows and into the spotlight.”

So as I said, Polaris is no slouch. It not only is a very bright star, but it also has two companions, and scientists are still studying it because it is unusual in other respects. We’ll talk about those other differences another month.

Events May 2012: Ring of Fire in the West, the fattest Moon, thinnest Venus, and parade of twins

I would love to see the May “ring of fire” – an annular solar eclipse, but it’s too far away for me. However, if you live anywhere near the eclipse path which starts in Asia and ends in the western United States, May 21/20 could prove special. Sky and Telescope says that while the eclipse weather for Asia tends to be bad at this time of year, the weather tends to be very good in the Western United States. And I have to admit, one of the little fascinations of this event for me is it starts on May 21 and ends on May 20 – yep, time can run backwards ;-).

Of course, if you’re not in the eclipse path,  May offers some other choice viewing for the unaided eye and binoculars :

But first, a few more eclipse notes

Path for the May annular solar eclipse. Click for larger image and for many more detailed eclipse maps, see the links a couple paragraphs down.

OK, it’s not time that’s running backwards – it’s the shadow of the Moon across the Earth and the shadow starts in Asia on May 21, eventually crosses the International Date Line, and then ends in Texas on May 20.  And – just to be clear – an annular eclipse  is not the same as a total solar eclipse, nor as a partial eclipse.

The annular eclipse is better than the typical partial eclipse – which is still fascinating – but it is not the stunner that a total solar eclipse is. It is “annular” – the word means “ring shaped” –  because the Moon is so distant from the Earth at the time of the eclipse that it is not quite large enough to totally cover the Sun and so there will be a ring of light – thus “ring of fire” – at “totality” which is probably better thought of as “mid-eclipse” since it won’t be total.  The Moon will cover  94% of the Sun’s diameter, but that remain 6 percent will still generate a lot of light. It will be noticeably darker at any given location during those few minutes most of the Sun is covered, but it will not be nearly as dark as when there is  a total  eclipse.

For a full selection of detail eclipse maps and other information for different sections of the world, please go here. And for far more detail on everything to do with the eclipse, go here.

It’s a BIG – I mean REALLY BIG – full moon!

As noted, the annular solar eclipse occurs because the New Moon in May is so far from the Earth and thus appears so small that it’s disk does not cover the Sun. On May 5, when the Moon is full, it is closest to us in it’s orbit – as close as it gets at the time of full Moon in 2012 and thus gives us an especially large full Moon.

How large is large? Well, when it rises on May 20th on the East Coast  of the U.S. it will be right near it’s minimum distance of 221,457 miles and will show a disc of roughly maximum size – about 33′ 30″ in diameter.

And on May 20, when it is creating the  annular eclipse of the Sun, it will be very close to it’s maximum distance from us of 252,712 miles and it’s disc will be roughly 29’24” in diameter. (Of course it will be too close to the Sun for us to see that night, but in the next few days the crescent will emerge and that crescent will  include a lunar disc shining by the reflection of light from the Earth and  an especially small one at that.)

Why the “roughly” and “abouts” for sizes and distance in those sentences? Because the Moon is constantly in motion and constantly changing size and distance from us. So while there’s a correct size and distance for a specific instant – such as Moon rise at my exact longitude – we have to be more general when we’re using numbers that cover a date and time for Moon rise over different parts  of the Earth, or an extended event like the annular eclipse.

So will you be able to tell that it’s big? I mean, if you do the math you will  see  that we’re talking of a change from largest to smallest of roughly  four minutes of arc.  Can we detect such a change? Yes. Look at the images below. See a difference?

The moon when closest – and farthest – from us. To simulate the experience of two Moon’s at these different distances from us, click on the image, print the resulting picture, and tape it to the wall 12 feet away from you.  (Images from Fourmilab, by John Walker
– public domain)

Unfortunately you never get to see such a comparison live, in the sky. In fact, you will have to wait until  Nov 28, 2012  to see the smallest full Moon this year.  At that time it will be right out there near it’s maximum distance from us and show a minimum disk size. (Hmmm… would be fun to photograph the May 5 Moon rise near a certain landmark, then do a similar photo at the same spot  on November 28. nut. of course, it would have to be a portable landmark you move into place because the two will not rise in the same location – in fact, they will be quite far apart.)

Now, if you want to crunch the numbers, consider four minutes of arc – that is frequently quoted as the distance we can detect with our naked eye. So, for example, two stars that are four minutes of arc apart and the same brightness we could split without optical aid. So why is it obvious the Moon is bigger when it’s a difference of just four minutes?  Remember that  with the Moon we’re citing a diameter, but what we see is an area. The area turns out to be 16.75 squared time 3.14 = 881  vs  14.7 square C 3.14=679 – a factor of 202 – nearly one fourth!  So if you calculate the area of the Moon’s disk visible to us when nearest and when farthest away the difference is significant!

There’s one caution, though.  The Moon and Sun when near the horizon always – ALWAYS – look much larger than they do when high in the sky. This has nothing to do with their  actual distance from us, or size. Take a picture of that Moon near the horizon and the picture will show a Moon that looks much smaller than you remember seeing.  The reason is what’s commonly known as the Moon Illusion – and that a whole different story. For a formal discussion of a complex topic, take a look here.

Complex as the Moon Illusion is, when you begin to understand the constantly shifting position of the Moon – develop a gut feeling by watching the changes – you really begin to appreciate the incredible complexity of landing a space mission there. And those with long memories will recall that  landing on the Moon is hardly a slam dunk.

In 1959 they [the Soviet Union] launched Luna 1, which missed the Moon by 3,728 miles (5,998 km). They followed that flight with a spectacular circumlunar orbit by Luna 3, which gave us our first pictures of the far side of the Moon.

 The development of probes in the United States also revolved around the Moon at this time. After several unsuccessful attempts to reach the Moon with the Pioneer series, the National Aeronautics and Space Administration (NASA) launched the Ranger series. It planned to crash-land the spacecraft onto the Moon’s surface, taking photos up until impact. The first few probes were unsuccessful, but the last three– Ranger 7, Ranger 8, and Ranger 9–took over 17,000 pictures beginning in 1963.   source

So this whole business of the lunar orbit around us is complex and is really better thought of as the Moon’s orbit weaving inside and outside our own in the course of each month  as we both travel around the Sun.  So I hope the weather cooperates and you get to bask in May’s full Moon and contemplate our deceptively simple relationship to our companion planet. (Yeah – that’s another thing – many regard the Earth and Moon more as a double planet system – the moons of other planets are much smaller in relation to their planet than our Moon is in relation to us.)

And now that we have the Moon on stage, how about that svelte Venus?

Venus goes through phases like the Moon as well. But what’s interesting about the Venus phases is that it is “full” when it’s farthest from us – and it’s a thin crescent when it’s closest to us. That really changes the dynamic. With the Moon there’s no such relationship. It can be a crescent and close, or a crescent and far away.

That thin crescent in May 2012  grows to more than 56″ in diameter by the end of the month.  Yes, those are seconds or arc. It’s still much smaller than the Moon where we measure it’s angular size in minutes. Remember, one minute equals  60 seconds, so the full Moon near the beginning of May is about 35 times as large as Venus is to our eyes near the end of May.  Can we see something this small as a crescent? I think it would be very difficult with the naked eye, but handheld binoculars will magnify it  7-10 times – that makes its crescent form identifiable.

BUT IF YOU PUT THIS TO THE TEST, PLEASE BE CAREFUL. VENUS RAPIDLY APPROACHES THE SUN THIS MONTH. So I suggest if you try to see it in daylight, you do so in the early part of the month. It is a crescent on May 1, though at 44″ a smaller one, it is still large enough to be detectable. JUST AVOID LOOKING AT THE NEARBY SUN WITH YOUR NAKED EYE AND/OR BINOCULARS OR A TELESCOPE.  For more details on how to safely see Venus in Daylight  go here.  On May 1, 2012 Venus is still about 36 degrees from the Sun.  By May 10, 2012  it’s about 30 degrees away and by the 20th it’s 20 degrees away. That is really getting too close for comfort as far as I’m concerned. In the second half of the month I would only look for Venus after sunset – even when taking the precaution of putting a building between me and the Sun.  I value my eyes far too much to play games.

But the point is. we have some interesting dynamics at work here in terms of its brightness. You would think Venus would be brightest when it was “full” or near full – just like our Moon. But it isn’t. And you might think it would be brightest when it is closest to us – but then it’s just a thin crescent that we see, so it isn’t.  Actually, there’s a compromise position about one third of the way through May 2012 when it is both a crescent – less than 20% of the disc illuminated – and near it’s brightest at magnitude -4.7. After that it gets to be a larger crescent, but it also dims some because so little of the disk is lit. Still, even at the end of the month with just one percent illuminated it is shining at a dazzling  – 4.1.

But I  hasten to add that in that last week Venus will be more and more difficult to see. Fifteen minutes after Sunset it is just five degrees above the horizon ( at my mid-Northern latitude) and in the bright twilight would require a clear and unobstructed western horizon to see.

This plunge towards the Sun, is, of course, heading for that twice-in-a-century event, the Venus transit of the Sun.  We already had a shot in 2004 at a transit of Venus, but these events come in pairs. The June 5, 2012 transit is the second of the pair for this century.  I’m really looking forward to this one. For North America, only the first part of the transit will be visible with sunset interrupting it. Weather prospects are pretty problematic too.  I plan to set up special equipment, properly filtered for safely viewing the Sun, in my favorite location with an unobstructed western horizon. But I’m also scouting other locations within reasonable driving distance, if the weather looks more favorable  north or west of here. I’ll publish a separate post with more details for viewing the transit which will be widely available from different locations on Earth and provides a way to relive some wonderful scientific history. In the 18th and 19th centuries viewing a transit of Venus was regarded as the key that would open the door to being able to calculate the actual size of our solar system. That provided the impetus for some fascinating – and downright heroic – scientific expeditions around the world.

May’s Parade of Twins – Saturn/Spica, Mars/Regulus and the Real McCoy!

The “Heavenly Twins,” Castor and Polux are still with us in May, high in the West an hour or two after Sunset. But they are joined by two other closer pairs of bright “stars” that have a special fascination do to color contrast and motion. High in the southeast are  Saturn and Spica.  And high overhead and favoring the southwest are a third pair, good as such only for the start of the month, Mars and Regulus.

Click image for larger version of this chart – prepared from Starry Nights Pro screen shot.

The pairs present some really nice color contrast , something that will be more apparent if you look at them in binoculars. Saturn has a yellowish tint, while it’s companion, Spica, is an icy blue. Mars is orange-to-red, while Regulus is white with just a hint of blue. Castor is white, but Pollux has a yellow tint.  (For more on the color of stars, please go here.)

Quite a line-up, really, since all are very bright “stars.”  Castor, while bright, is the dimmest of the six.  It is magnitude 1.56 and the convention is to say that first magnitude  runs from magnitude .5 to magnitude 1.5.  So Castor  misses first magnitude  by hair where the others are either first magnitude or zero!

Pollux is magnitude 1.15.  Saturn starts the month at magnitude .5, then joins the zero magnitude class by climbing to magnitude .3  by the end of the month.  And Mars? Mars is the most fickle  of the group. It starts off the month a perfect 0 magnitude, but by the end has dimmed to .5, so it’s headed for the first magnitude class. It also breaks the twin pattern – that is, at the start of the month it is is less that 6 degrees from Regulus (magnitude 1.34), but it more than doubles that distance by the end of the month.  Saturn barely changes it’s relationship with Spica (magnitude .96), being about 4°50′  distance all month – and, of course, Castor and Pollux are, for all practical purposes, constant at a separation of 4°30′.

Look North: May is the month Polaris gets two bright flankers!

Click for larger image. (Developed from Starry Nights Pro screen shot.)

Click here to download a printer-friendly version of this chart.

Is the North Star – Polaris – our brightest star? No! And it certainly won’t look that way this month as it shares the northern sky with two very bright stars. But, read on. Polaris is not nearly as dim as it looks!

If you have been learning your guidepost stars as they rise in the East, you won’t be surprised by the two bright stars which flank – and outshine – our pole star in May. To the northwest is Capella, a star we first met when it rose in the northeast in November. In May the northeast is dominated by a star that is almost Capella’s twin in brightness, Vega, a guidepost star we introduce in May. (See “Look East!” for more about Vega.) As a bonus we also have the twin guidepost stars, Castor and Pollux, coming into view high above Capella, as we face north. But let’s focus on Capella and Vega.

New star watchers frequently assume the North Star, Polaris, will be the brightest star in the sky. It isn’t even close! It is bright, but its fame comes because it’s very, very close to where the axis of the Earth points to the north celestial pole. So it serves anyone trying to find true north as a very good guide. But when it comes to brightness, it’s in the same league as the stars in the Big Dipper. Quite bright, but it can’t hold a candle to Capella and Vega. When you look at a list of the brightest stars, Vega is number 5 and Capella number 6. Polaris, our North Star, is number 48!

As simple as one, two, three!

That doesn’t mean Polaris is a slouch, though. First, in the eastern sky in May you meet Spica. (That’s on our chart for the east.) One distinction of Spica is that it’s as close to being magnitude 1 as any star gets. A distinction of Polaris is, as Spica defines magnitude 1, Polaris defines magnitude 2. (To be precise it’s magnitude 2.02.) Vega and Capella are extremely close to magnitude 0. Vega is 0.03 and Capella 0.08. Good luck on telling the difference! This month, if you look north 90 minutes after sunset, you may think Capella is a bit brighter actually – but if it appears that way it will be because it’s a bit higher in the sky and thus is not dimmed by having to fight its way through as much of our atmosphere as Vega is doing at the moment. So don’t try to split hairs. And yes, you’re right – they are NOT really as “simple as one, two, three” – on the magnitude scale they are as simple as zero, one, two – but that didn’t sound as good! (Vega and Capella are zero; Spica is magnitude one, and Polaris, magnitude two.)

So which is really the brightest star of these four? Are you ready for this? Polaris! That’s right – if you put all four stars at the same distance, Polaris would appear to be the brightest. Remember, that the lower the magnitude number, the brighter the star. In absolute magnitude, these four stars line up this way:

  • Polaris -3.4
  • Spica -3.2
  • Capella 0.1
  • Vega 0.3

And those absolute magnitudes also reflect their order in distance from us.

  • Polaris 433 light years
  • Spica 250 light years
  • Capella 45 light years
  • Vega 25 light years

So sometimes a star is very bright because it’s – well, very bright. But sometimes it only appears to be very bright because it is very close to us. If you put our closest star into this group, our Sun – remember, it is just 8 light minutes from us – in absolute magnitude it would be by far the dimmest of this group – absolute magnitude 4.9! So while Polaris doesn’t look all that bright, it really is a very bright star! Another way to think about this is if you move our Sun out to where Polaris is, it would be about magnitude 10. You would need a binoculars or a telescope to see it!

Click image for larger view of this chart. Yellow circle represents typical field of view for low power binoculars, such as 10X50.

To get an idea of the difference between Polaris and our Sun, point your binoculars towards Polaris.  You should be able to make out the “Engagement Ring” asterism – granted, a crude ring with Polaris as the diamond.  This asterism points you towards the true north celestial pole on the other side of Polaris and also gives you a good idea of about how far Polaris is from that pole.  Small binoculars will not show you the companion of Polaris, but to get an idea of how bright a our Sun would be at the same distance, look for the star labelled 9.8 – and if you can’t see it, see if you can see the star that’s a bit brighter labelled “9.”  Don’t expect to see these instantly. Sit calmly, relax, and keep looking for at least a minute.

And here’s one more cool secret about Polaris. It has a companion that just happens to be quite dim – magnitude 9. It’s fun to see the two of them if you have a small telescope, though it’s not all that easy because Polaris is so much brighter than its companion. But if you get a chance to see Polaris and its companion in a telescope, remind yourself that the very faint companion is still a bit brighter than our Sun would look at this distance. This companion, known as Polaris B, was discovered in 1780 by William Herschel, and for many years Polaris was thought to be a binary star – that is, a system of two stars orbiting about a common center of gravity. But Polaris was holding one more surprise – it’s really a triple star.

The top image shows Polaris and its faint companion that can be seen in any decent backyard telescope. The bottom image shows the second companion, Polaris Ab, which has only been seen by using the Hubble Space Telescope.

This has been known for some time, but no one could see the third star until they turned the Hubble Space telescope on it in 2006. That’s when NASA released the first image of this third companion. The accompanying press release explained it this way:

By stretching the capabilities of NASA’s Hubble Space Telescope to the limit, astronomers have photographed the close companion of Polaris for the first time. They presented their findings  in a press conference at the 207th meeting of the American Astronomical Society in Washington, D.C.

“The star we observed is so close to Polaris that we needed every available bit of Hubble’s resolution to see it,” said Smithsonian astronomer Nancy Evans (Harvard-Smithsonian Center for Astrophysics). The companion proved to be less than two-tenths of an arc second from Polaris — an incredibly tiny angle equivalent to the apparent diameter of a quarter located 19 miles away. At the system’s distance of 430 light years, that translates into a separation of about 2 billion miles.

“The brightness difference between the two stars made it even more difficult to resolve them,” stated Howard Bond of the Space Telescope Science Institute (STScI). Polaris is a supergiant more than two thousand times brighter than the Sun, while its companion is a main-sequence star. “With Hubble, we’ve pulled the North Star’s companion out of the shadows and into the spotlight.”

So as I said, Polaris is no slouch. It not only is a very bright star, but it also has two companions, and scientists are still studying it because it is unusual in other respects. We’ll talk about those other differences another month.

Look East! Slide down to Saturn and Spica in May 2012!

It’s a tad easier to find Saturn and Spica if you found Arcturus in April, but if not you’ll simply get a “two-for-one-special” for your effort this month. As always, start about 45 minutes to an hour after sunset. In May 2012 there should be four bright “stars” in the East, but one is a planet. In order from north-to-south they are Vega, Arcturus, Saturn, and Spica. As the sky gets darker the bright stars of the Big Dipper, high in the northeast, will guide you.

All you really want is the three stars of the Dipper’s handle. It forms a wonderful arc, and if you follow the curve of that arc, it will always take you to Arcturus. Continue the same curve for about the same distance, and you will come to the beautiful – but fainter – blue-white gem, SpicaSaturn is very close to Spica, though yellowish, compared to the rich lue of the star. And Vega is way at the other end – just coming up in the northeast. It is very close to the same brightness as Arcturus. All of which, I’m sure, is much easier to grasp if you simply look at this month’s “look east” chart.

Notice that the distance between the last star in the handle of the Big Dipper and Arcturus is almost exactly the same as the distance between Arcturus and Spica - a good way to make sure you're looking at the right star! Also note the movement of Saturn from 2011 to 2013. Click image for larger version. (Developed from Starry Nights Pro screen shot.)

Click here to download a printer-friendly version of this chart.

We dealt with Arcturus last month. Saturn will be in our sky most of the night and as always is a treat for the small telescope user. From a naked eye perspective,  it’s fun to remember that the name “planet” means “wanderer” in Greek, but all “wanderers” are not created equal. Mars, Venus, and Mercury move  so quickly in our night sky that you can easily mark their changes over a period of a few days -certainly a week.  Saturn is much more sluggish.

Look at the chart and you’ll see how little Saturn changes position over the course of an entire year – it moves roughly 12 degrees.  To see this,f ind Saturn. Hold your fist at arms length so Saturn is just below it. Just above your fist is where Saturn was last year. Put Staurn on top of your fist and just below your fist is where it will be next year. So how long will it take Saturn to get around the sky to roughly the same position? Well, 360/12 = about 30 years!  Now if you think a moment, the Moon takes about 30 days to get around our sky – and that means the Moon moves each day about 12  degrees –  the same distance covered by Saturn each year.  All of which should tell you that it would be reasonable to assume Saturn is much farther away from us than the Moon – which, of course, it is.

None of this is rocket science or in any way  profound, but I find it interesting to contemplate as I look up and see Saturn. I measure that distance it will travel in the next year and in my mind’s eye I perch above the Solar System and I see a long thin pie slice reaching from me to Saturn’s distance orbit and this helps me keep things in perspective – gives me a better intuitive feel for the neighborhood in which we live.  OK – for the record Saturn is moving at about 22,000 miles an hour, Mars about 54,000 miles an hour in a much shorter orbit, and we’re whipping right along close to 67,000 miles an hour – and we don’t even feel the wind in our face! Oh – and Saturn’s actual orbital period is 29.458 years.

On to this month’s new guidepost stars!

Vega and Spica are each fascinating stars, but let’s start with Vega. Shining brightly not far above the northeastern horizon as the evening begins, Vega comes about as close to defining the word “star” as you can get. In “The Hundred Greatest Stars” James Kaler calls it “the ultimate standard star” because its magnitude is about as close to zero as you can get (.03) and its color is about as close to white as you can get. (If you’re one of those who assumed all stars are white, you’re forgiven. Individuals vary in their ability to see different colors in stars and for everyone the color differences are subtle – in fact I think of them as tints rather than colors. )

It’s hard not to be attracted to Vega when you read Leslie Peltier’s wonderful autobiography, “Starlight Nights.” Vega was central to his astronomical observing throughout his career because he began with it when he first started reading the book from which I got the idea for this web site, “The Friendly Stars” by Martha Evans Martin. Peltier wrote:

According to the descriptive text Vega, at that very hour in the month of May, would be rising in the northeastern sky. I took the open book outside, walked around to the east side of the house, glanced once more at the diagram by the light that came through the east window of the kitchen, looked up towards the northeast and there, just above the plum tree blooming by the well, was Vega. And there she had been all the springtimes of my life, circling around the pole with her five attendant stars, fairly begging for attention, and I had never seen her.

Now I knew a star! It had been incredibly simple, and all the stars to follow were equally easy.

Vega went on to be the first target of the 2-inch telescope he bought with the $18 he made by raising and picking strawberries. (This was around 1915.) And Vega became the first target for every new telescope he owned until his death in 1980. If you still don’t know a star, go out and introduce yourself to Vega early on a May evening. Even without a plum tree to look over, you can’t miss her! And once you’ve done that you’re well on your way to making the night sky your own.  (And yes, Vega is the star from which the message comes in Cal Sagan’s book/movie “Contact.”)

Vital stats for Vega, also known as Alpha Lyrae:

• Brilliance: Magnitude .03 ; a standard among stars; total radiation is that of 54 Suns.
• Distance: 25 light years
• Spectral Type: A0 Dwarf
• Position: 18h:36m:56s, +38°:47′:01″

Spica, a really bright star – honest!

Spica is truly a very bright star, but the numbers you may read for its brightness can have you pulling your hair. That’s because there are at least four common ways to express the brightness of Spica and other stars, and writers don’t always tell you which way they’re using. So let’s look at these four ways and see what they mean for Spica.

The first is the most obvious. How bright does it look to you and me from our vantage point on Earth using our eyes alone? We then assign it a brightness using the magnitude system with the lower the number, the brighter star. (For full discussion of this system, see “How bright is that star?”)

By this measure Spica is 16th on the list of brightest stars and is about as close as you can come to being exactly magnitude 1. (Officially 1.04)Thopugh I should add here that the number really marks the midpoint of a magnitude designation – that is, any star that is in the range of magnitude .5 to magnitude 1.5 is called “magnitude 1” and so on for the other numbers ont he scale.

But that scale talks about what we see. It doesn’t account for distance. Obviously if you have two 60-watt light bulbs and one is shining 6 feet away from you and the other 1,000 feet away, they are not going to look the same brightness. But if we put them both at the same distance – say 100 feet – they would look the same. So it is with stars. To compare them we pretend they all were at the same distance – in this case 10 parsecs, which is about 32.6 light years. Put our Sun at that distance and it would be magnitude 4.83. (That’s about as faint as the fainest stars we see in the Little Dipper.) We call that its absolute magnitude.

The absolute magnitude for Spica is -3.55 – not quite as bright as dazzling Venus.

Wow! That’s pretty bright compared to our Sun! Yes it is. Sun 4.83; Spica -3.55. Don’t miss the “minus” sign in front of Spica’s number! That means there’s more than eight magnitudes difference between the Sun and Spica. And that relates to the next figure you are likely to see quoted. Something that is called its luminosity. Luminosity compares the brightness of a star to the brightness of our Sun. Unfortunately, the term is often misused – or poorly defined. Thus in the Wikipedia article I just read on Spica it said that “Spica has a luminosity about 2,300 times that of the Sun.” Yes, but what does that mean? It means that if we were to put the two side by side, Spica would appear to our eyes to be 2,300 times as bright as our Sun.

That is bright! But there’s more, much more. Spica is also a very hot star – in fact one of the brightest hot stars that we see with our naked eyes. But we miss most of that brightness because most of it is being radiated in forms of energy that our eyes don’t detect. In the case of Spica, that is largely ultraviolet energy. The Wikipedia article actually listed Spica’s luminosity twice, and the second time it gave it as “13,400/1,700.”

Oh boy – now we have Spica not 2,300 times as bright as the Sun, but more than 13,000 times as bright. Now that IS bright – but is it right? Yes! So why the difference? Again, the first “luminosity” given – 2,300 times that of the Sun – is measuring only what we can see with our eyes. The second is measuring total amount of electromagnetic radiation a star radiates and is properly called the “bolometric luminosity.” And why two numbers for that last figure? 13,400/1,700? Because while Spica looks like one star to us, it is really two stars that are very close together and one is much brighter than the other. So what we see as one star is really putting out energy in the neighborhood of 15,100 times as much as our Sun.

This can get confusing, so I suggest you remember three things about Spica.

1. It defines first magnitude, having a brightness as it appears to us of 0.98 – closer than any other star to magnitude 1.

2. It is really far brighter (magnitude -3.55), but appears dim because it is far away – about 250 light years by the most recent measurements.

3. It is very hot – appearing blue to our eyes – and because it is very hot it is actually radiating a lot more energy in wavelengths we don’t see, so it is far, far brighter than our Sun.

Spica is the brightest star in the constellation Virgo, one of those constellations where you can not really connect the dots and form a picture of a virgin unless you have an over abundance of imagination. Besides, the remaining stars are relatively faint. That’s why we focus on the bright stars and sometimes those simple patterns known as “asterisms” and use them as our guides.

Vital stats for Spica, also known as Alpha Virgo:

• Brilliance: Magnitude .98 ; as close to magnitude 1 as any star gets; a close double whose combined radiation is the equal of 15,100 Suns.
• Distance: 250 light years
• Spectral Types: B1,B4 Dwarfs
• Position: 13h:25m:12s, -11°:09′:41″

Guideposts reminder

Each month you’re encouraged to learn the new “guidepost” stars rising in the east about an hour after sunset. One reason for doing this is so you can then see how they move in the following months. If you have been reading these posts for several months, you may want to relate Spica to two earlier guidepost stars with which it forms a right triangle, Arcturus and Regulus. Here’s what that triangle looks like.

Click image for larger view. (Created, with modifications, from Starry Nights Pro screen shot.)

Click here to download a printer-friendly version of this chart.

Once you have identified the Right Triangle, note carefully the positions of Spica and Regulus. They pretty much mark the “ecliptic.” This is the path followed by the Sun. Also, within about 9 degrees north or south of it, you will find the planets and the Moon. That’s well illustrated in 2012 by the presence of both Saturn and Mars, very near the ecliptic, as noted on our chart.

Arcturus and Regulus are not the only guidepost stars and asterisms in the May sky. Again, if you have been reading these posts for several months, be sure to find the stars and asterisms you found in earlier months. Early on a May evening these will include, from east to west, the following: Arcturus, Spica, Saturn, Leo’s Rump (triangle), The Sickle,  Mars, Regulus, the Beehive, Procyon, Sirius, Pollux, Castor, and in the northwest near the horizon, Capella, and the Kite. Venus will be a bright evening “star” in the west, and if you look early in the month you may catch a glimpse of Sirius and Betelgeuse before they set.

Close encounters of the Venus kind! March, April, May, June 2012 – Mark your calendar!

(Go here for a personal update on observing this even – with pictures.)

Venus is a visual treat any night – and for that matter day –  this spring, dazzling us in the western sky right after Sunset as it puts in it best performance of this year and has close encounters with the Moon, the Pleiades, and finally the Sun itself. This last is a once-in-a-lifetime-appearance – the other events are less rare, but, of course, the weather has to cooperate.  Nothing is needed for most of these experiences but your naked eye, though binoculars help and a small telescope makes it even more fun. The last event – the encounter with the Sun – does require a telescope and one with a special filter to make viewing safe.

Here’ s a quick visual guide to Venus events, followed by a guide on how to find Venus in broad daylight – no kidding – and what’s more, late March through April is the best time to try to see this brilliant planet at mid day! I’ll update this post for May. Please note, the charts are specific to my location which makes them generally best  for the East Coast of the US. You can see this show from anywhere in the world, but the exact positions of Venus and the Moon on any given evening will vary somewhat depending on your latitude and longitude.

March 25, 2012

About 10 degrees separate Jupiter from Venus and Venus from the Pleaides - but the Moon and Jupiter should fit in the same low power binocular field, as should the Moon and Venus on the next night. Prepared from Starry Nights Pro screen shot - click to enlarge.

March 26, 2012

About 10 degrees separate Jupiter, Venus, and the Pleaides - but the Moon and Venus should fit in the same low power binocular field, as didthe Moon and Jupiter on the previous night. Prepared from Starry Nights Pro screen shot - click to enlarge.

March 27, 2012

Jupiter, Venus, and the Moon form a nice line that marks the ecliptic - the plane of our solar system, and if you look to the East you'll see this path completed by Mars. Prepared from Starry Nights Pro screen shot - click to enlarge.

April 2, 3, and 4 – a once-in-eight-years encounter between Venus and the Pleaides!

You really need binoculars to see this because the glare of Venus will mask the most beautiful of star clusters, the Pleiades. The encounter will be best on April 3 - but nice the night before and after. Click to enlarge. Prepared from Starry Nights Pro screen shot.

Venus gets near the bright stars of the Pleiades every eight years. This year it will pass through the south side of the cluster, which means that on April 3 , using binoculars, you should be able to see Venus to the left of the four core bright stars in the cluster.  The mythological implications are staggering – I can see the headlines in Ancient Greece now –  Goddess of Love Meets Seven Sisters!  Here’s how Wikipedia sums up their sex lives:

Several of the most prominent male Olympian gods (including Zeus, Poseidon, and Ares) engaged in affairs with the seven heavenly sisters. These relationships resulted in the birth of their children.

  1. Maia, eldest of the seven Pleiades, was mother of Hermes by Zeus.
  2. Electra was mother of Dardanus and Iasion, by Zeus.
  3. Taygete was mother of Lacedaemon, also by Zeus.
  4. Alcyone was mother of HyrieusHyperenor and Aethusa by Poseidon.
  5. Celaeno was mother of Lycus and Eurypylus by Poseidon.
  6. Sterope (also Asterope) was mother of Oenomaus by Ares.
  7. Merope, youngest of the seven Pleiades, was wooed by Orion. In other mythic contexts she married Sisyphus and, becoming mortal, faded away. She bore to Sisyphus several sons.

April 22, 2012

The late April show may not have all the appeal of the one in late March, but it's still nice. You will probably need binoculars to pick out Jupiter, even though it is still quite bright. Prepared from Starry Nights Pro screenshot - click to enlarge.

April 24, 2012

On April 24, 2012 the Moon splits Aldebaran and Venus, though Aldebaran may be hard to see despite being a first magnitude star, so you may have to use binoculars. Prepared from Starry Nights Pro screenshot - click to enlarge.

April 25, 2012

On April 25, 2012 the Moon is still close enough to Venus to make an interesting combination. Prepared from Starry Nights Pro screenshot - click to enlarge.

May 22, 2012

On May 22, 2012 the situation looks much different.  Venus is now getting much closer to the Sun – remember it has a date with the Sun in early June – but it still gives us one more nice combination with the Moon. Again, unobstructed western horizon is important.  The other stars named in the chart are all bright “guidepost” stars but may be difficult to see in strong twilight – however, they will be the first to appear as twilight fades. Prepared from Starry Nights Pro screenshot – click to enlarge.

June 5, 2012 – Once-in-a-Lifetime Show – Venus transits the Sun

As I wrote in January

So circle June 5, 2012. What is a transit of Venus? It’s a time when we can see Venus as a black dot cross the disc of the Sun – a time when Venus is actually between us and the Sun – and it happens rarely.  There have been just seven such transits since the invention of the telescope! And – of course – be careful! You will need special equipment to observe such a transit. Never look at the sun either with your naked eye or any  binocular or telescope unless it is one especially equipped just for looking at the Sun.  Such equipment isn’t expensive, though, and if you already have a telescope, would be a good investment to consider for this event and to regularly see  sunspots. I’m sure there will be several public observation points set up for those who don’t have such a telescope.

More details will be provided in May.

Orrery View – why we see what we see – the dance of the Moon and planets

The dance between the  bright planets and the Moon is always fascinating, but made all the more so if you understand what is going on back stage – why we see what we see.  To do that, I suggest you study the following Orrery views taken from the Solar System live web site. Take care to note the line of sight between earth, a given planet, and the Sun.  Everything is in motion,of course, but the motions that count the most for the changes we see in our Western sky right now from night-tonight are these:

  • The  moon moves about 12 degrees – more than our extended fist – each evening because of its orbit around the Earth.
  • Venus moves relatively quickly, so it’s change of position is a combination of its own movements and the motions of the Earth as we both circle the Sun.
  • The changes in how we see Jupiter are primarily caused by our own motiona round the Sun. Jupiter is in motion, but it is slower and so far away that it takes weeks, if not months to notice its motion against the background of stars. However, as with the stars, it’s position change a little each night because of the motion of the Earth.

And on June 5, 2012 – the day that Venus will transit the Sun, here’s a close-up view of the line-up of Venus, Earth, and the Sun.

In April 2012 you can meet the Goddess of Love in broad daylight – no fooling!

Actually, you can do it right now. We’re talking Venus, here, and our sister planet is so bright even in March that you can see it with the naked eye in the middle of a clear day! All you have to do is know when and where to look – and please, please avoid the nearby Sun!

What’s more, April is the best time to look for it this year because this is the month when it is at its brightest and also near it’s greatest distance from the Sun. That great distance makes it easier to see – and safer.

Here’s how. On a clear day look for Venus in the path the Sun took across the sky, but about forty -five degrees behind it. (Use your fist to get a rough idea, remembering one fist, held at arms length, is about 10-degrees.) Use binoculars and once you spot it and know exactly where to look, use your naked eye. And play it safe by leaving the Sun blocked from sight by a nearby building, tree, or other obstacle.

OK -let me expand on those instructions and give you some specifics and hints of how best to do this.

First – the day should be clear – really clear with the bluer the sky the better. Not all “clear” days are equal. Astronomers are looking for “transparency” as well, which means you don’t want a milky, white sky.

 Second – You should know that Venus follow the same general path as the Sun does across the sky – sometimes behind it (as now), and sometimes ahead of it. Usually Venus is too close to the Sun to easily – and safely – pick out. But this April – and for that matter the end of March – it well be separated from the Sun by about 45 degrees – the most it will be all year.

 Third, pick your viewing location carefully.  Everyone should know not to look at the Sun, but I don’t want your enthusiasm for seeing Venus in daylight to lead to an accidental viewing of the Sun – and besides, this will make the seeing easier. STAND ON THE EAST SIDE OF A BUILDING AFTER THE SUN HAS PASSED SO EVEN IF YOU ACCIDENTALLY LOOK TOWARDS THE SUN, YOU WON’T SEE IT!

Fourth, pick your time – generally from noon until sunset, but I think the best time will be when Venus is highest in the sky – near what is called it’s “transit.”  That gives you a good place to look – due south and roughly at the same altitude as the Sun was at around noon.  In April, 2012, Venus transits about three hours after the Sun. In other words, if you know when the Sun is at its highest point – locally, for me, that’s close to 1 pm on April 1 – then Venus will be coming along to the same point about three hours later – about 4 pm.

Fifth – begin your search with binoculars – any binoculars will do, but generally one with low power and thus a reasonably wide field of view.  And one caution. You will systematically scan the correct area of sky – but do your scanning slowly. I was out testing this the other day and found it was very , very easy to see Venus in binoculars – yet I missed it over and over again because I was scanning too fast!

Could I see it with the naked eye  in March? No. Not on the three days I looked and saw it in binoculars.  Maybe the days just weren’t clear enough – there was a lot of moisture in the air. And maybe my old eyes are just not keen enough for this sort of thing.  But I did see Venus this way several years ago and it’s one of those sights that when you first find it, you can’t believe you were missing it.

The best hint I’ve read for this – and this is true with binoculars as well as your eyes – first focus your binoculars on the  most distant object you can see – hopefully something a good half mile or more away away. That way they’ll be roughly in focus to pick up Venus.  (You can even do this the night before by focusing them on a star.)  And when you’re searching with the naked eye? Do the same thing. Focus your eyes on some distant object, THEN look up for Venus. (Our eyes tend to default to a near – or nearer – focus point if we’re not careful. )

It’s always cool to see a bright planet – but it is so much cooler to see a bright planet in broad daylight – even with binoculars Venus will be a sparkling white diamond against a beautiful blue sky.

Events: The planets in May 2011: Everyone’s at the party!

May offers a planet spectacular in three parts – first, the evening show where Saturn  meets the stunning double star, Porrima; then the full morning show where the rest of the the planets gather, and then the pre-dawn special, which Sky and Telescope magazine calls “the most compact visible gathering of four bright planets in decades.” Here’s a summary in pictures of each of these events with links at the end of each summary for more details and many more charts

Saturn Kisses Porrima

Here’s a simulation of Saturn’s dance with Porrima over the next two months, prepared with Starry Nights Pro software.

For the naked eye observer, watching Saturn and Porrima during May and June of 2011 provides a terrific opportunity to see a planet in retrograde motion – then pause,  then swing back in its normal eastward path against the background stars.  For the small telescope user it’s even better.  Porrima is a stunning double star when seen in a back-yard telescope – and Saturn, with its rings, the most awesome planet in a small telescope. During May and June of 2011 the pair come amazingly close – so close they’ll both fit in the same telescopic field of view near the end of May and in early June. For more details, go here.

The Full Morning Show

This shows you where six of the seven visible planets are in the eastern pre-dawn sky about 30 minutes before sunrise - however, to find Neptune and Uranus you'll have to look earlier when the sky is darker. And please - click this image for a larger view! (Prepared from Starry Nights Pro screen shot.)

Frankly, Neptune and Uranus will be easier to see later this year, but if you’re getting up early to see the pre-dawn gathering of four planets very close to one another, then why not get up a couple of hours earlier and do a search for the outer two planets, Uranus and Neptune? You’ll need binoculars, an unobstructed eastern horizon, and clear skies, of course. For more details, go here.

The Pre-dawn Special Show

Jupiter, Venus, Mercury, and Mars, as seen in the predawn sky of May 11 from mid-northern latitudes. I've modified this Starry Nights Pro screen shot to include images of the planets to scale - a reminder of what these faint morning "stars" actually look like up close and personal. Click image for a much larger version.

As mentioned, May’s pre-dawn skies brings us what Sky and Telescope calls “the most compact visible gathering of four bright planets in decades.” And it goes on most of the month! The best seats in the house for this show will be to the south – the farther south the better. Those of us in mid-northern latitudes will find it more challenging to see this  pre-dawn show, and for all an unobstructed eastern horizon and exceptionally clear weather is a must. If I’m hoping for one morning of exceptionally clear skies it would be for May 11 – but fortunately the show starts well before then and continues well after that date. Go here for more details and many more charts.

Saturn Kisses Porrima – the details!


The outer planets generally appear to move eastward against the backdrop of distant stars. However, as Earth overtakes a planet in its orbit and passes it, the planet appears to move backwards – westward – called retrograde motion.  Watch Saturn during May and June to see this change in reverse, for in this case during May Saturn is already in retrograde (westward) motion. Then in the first two weeks of June it appears to halt, stand still, then reverse itself to resume  eastward motion.  Though Saturn’s motion is very slow – it takes 29.5 of our years to complete a trip around the Sun – its motion is easy to mark this year as you note its changing relationship to the bright (magnitude 3.4) star Porrima.  This you can do with the naked eye, but the changes will be easier to see if you use binoculars and make a little chart.  At the start of May Saturn is about 1.5° from Porrima. By the end of the month it’s separated  from Porrima by less than 20 minutes of arc – about one third of a degree. During the first few days in June it will appear to stand still, then will slowly resume its eastward motion, putting more and more distance between it and Porrima. To observe all this, start with this chart, use your binoculars, and note its changing position. (You don’t have to start on May 1 – any day this month will do – but it will be good if you can check every week or so and draw in the changing position of Saturn. )

Here are Saturn and Porrima at the start of the month. Saturn is the brightest "star" at magnitude 0.54 and Porrima the next brightest at Magnitude 3.4. There are a couple of other stars in the field that are magnitude 6 and the rest should be visible in binoculars if you look carefully. Note: Porrima is always to the west of Saturn - but early in the evening it will feel more like it is "above" Saturn. Remember - west is the direction everything appears to move as the night goes on. Click image for a larger version. (Prepared from Starry Night Pro screen shot.)

To keep track of Saturn’s changing position night-to-night and see it  switch directions,  download this “printer friendly” version of the above chart.

For observers with telescopes this should make a stunning sight – especially during the first week of June. The trick will be to use an eyepiece that gives you enough magnification to split the very close pair of stars that is Porrima, yet include Saturn in the same field of view.  I’m planning to use a 4-inch refractor and a wide-field eyepiece delivering at least 150X. I’m honestly not sure if that will be enough – depends on conditions.  On April 29 I could fit the pair comfortably in a low power (22.5X) field. I could not get a clean split of Porrima at any power because the air was too turbulent. In theory I should be able to see both Saturn and a clean split of Porrima near the end of the month or in early June, but the weather will have to cooperate!  Not being sure if it will work is all part of the fun. You can read all about Porrima and how to split it in my friend John Nanson’s post on the star-splitting blog we share. Check it out here!

Incredibly, Porrima was apparently named for two sisters who were goddesses of prophesy. Since the name was given before they could possibly tell that Porrima was two stars, that’s sure some prophesy! If that’s the case, I’m sure we can assume Saturn – the Roman god of agriculture – is playing the shy farm boy,  giving them both a kiss,  then running. 😉

The Full Morning Show – in detail!


Finding Uranus and Neptune requires an early start in May, but with patience, both can be located using binoculars, though Neptune is a challenge because of its dimness and  Uranus because it’s still close to the horizon when it is dark enough to see. Let’s start with Uranus.

Finding Uranus - First see if you can locate the Circlet of Pisces about one fist above the eastern horizon and consisting of 4th and 5th magnitude stars. Binoculars will probably be needed for this. Click chart for larger view. Prepared from Starry Nights Pro screen shot.

Step 1 – The challenge in finding Uranus is you need a dark sky – but the planet is just getting high enough to view as astronomical twilight – the first hint of dawn – begins. So you might start looking for the circlet of Pisces about two hours before sunrise and after you locate it, look closer to the horizon for Uranus.  The Circlet consists of five stars that are about as bright as the four fainter stars in the Little Dipper. There are two others included in our chart and these are even fainter. The whole asterism may be just a little too large to fit in your binoculars. Here’s a printer friendly version of this first chart.

Step 2: The circle covers five degrees - about what you see in binoculars. Notice the distinctive trapezoid asterism to the left? That should serve as a good guide. Uranus will be just slightly brighter than the stars of this trapezoid. Click image for larger view. (Prepared from Starry Nights Pro screen shot.)

Step 2 – Between the Circlet of Pisces and the eastern horizon you should find Uranus about an hour before sunrise – but start looking a bit earlier. The sky will be getting brighter making it difficult to spot this magnitude 6 planet, even with binoculars.  Here’s a printer-friendly version of the above chart.

Finding Neptune

Finding Neptune is easier because it’s higher than Uranus while the sky is still fully dark. But at magnitude 7.9 it is significantly fainter and as far as I’m concerned it’s in a celestial wilderness where the constellations are not much help and there is little in the way of bright asterisms to point the way. But for those who enjoy a challenge, here are a couple of charts. The first is a broad overview and gives you an idea of the general territory. For me the most recognizable feature is the Great Square of Pegasus, but that’s pretty far away. Closer – but fainter – will be the Circlet of Pisces included on the Uranus chart.

This chart will just give you an idea of the general region in which to search for Neptune on May mornings about two hours before sunrise. Click image for much larger - and readable - version. (Prepared from a Starry Nights Pro screen shot.)

This is Neptune at mid-month. It is moving from right to left, but very slowly, so the chart is good for the month, just understand the position may not be exactly what you see here. Click image for larger version. (Prepared from Starry Nights Pro screen shot.)

Download a printer-friendly version of this chart.

Guide to the early morning planet show – in detail!


OK, it’s worth repeating – Sky and Telescope magazine calls this “the most compact visible gathering of four bright planets in decades.”  The farther south you go, the easier this show will be to see, but the general rules apply to all locations.

Where you are and when you look is important!

The further south you are the higher the planets will be at any given instant and the higher they are the earlier you can look. The earlier you look, the darker the sky background, making the planets easier to find.

Binoculars are a critical aid.

Nothing special is needed – any binoculars will help – but when trying to see the fainter of these planets – Mercury and Mars – binoculars are absolutely critical in northern latitudes and will help no matter where you are. DO STOP USING THEM 15 MINUTES BEFORE SUNRISE, HOWEVER. YOU DON’T WANT TO CHANCE LOOKING AT THE SUN WITH YOUR BINOCULARS. THAT IS DANGEROUS.  And if you haven’t seen the planets by 15 minutes before sunrise, you’re not going to see them – so just sit back and enjoy the dawn!

An unobstructed eastern horizon and clear skies are essential.

Your fist held at arm’s length covers about 10 degrees. In mid-northern latitudes the planets will not get above 10 degrees before it gets too light to see them.

Start looking early.

The charts that follow are for a time that strikes a balance between the altitude of the planets and the darkness of the background sky. But if a chart is for 30 minutes before sunrise, start looking at least 15 minutes prior to that – perhaps half an hour earlier. The planets will be lower then, of course, but in events such as these you are playing a game with the elements – the higher the planet, the easier to see – but as the planets gets higher, the sky background gets lighter and the lighter the sky background, the harder it will be to see the planets – so the right hand gives while the left hand taketh away!

How to know which is which.

The planets will change position each day, and as you will see from the charts below, the arrangement varies depending on where you are as well. So how do you know which is which?  Brightness will be your key. The brightest is Venus, the next brightest Jupiter, the next Mercury, and the dimmest Mars.  Mars will be the most difficult as it is both dim and low.

To get a feel for what a difference location makes, look at the next three charts. Note the latitudes – the first is for 42°N, the next for 26°N, and the last for 34° S. Also note that the first two are for 30 minutes before sunrise, while the last one is for an hour before sunrise.

30 minutes before sunrise – 42°N

Circle represents a 5-degree field of view. Most binoculars will show a bit more. Click image for larger view. Prepared from Starry Nights Pro screen shot.

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 30 minutes before sunrise – 26° N

Click here to download a printer-friendly version of this chart.One hour before sunrise - 34° SouthHere's the view from Sydney, Australia - note change in time and date. Circle represents a 5-degree field of view. Click image for a larger view. (Prepared from Starry Nights Pro software.)

Click here to download printer-friendly version of this chart.

Changing with date

These four  planets will provide an interesting, but challenging, tableau most of the month as the visual relationships change. Here’s a guide to those changes using charts  for every four days – all are for mid-northern latitudes and for about half an hour before sunrise.  No larger versions are provided, so don’t bother clicking on them and all are prepared from Starry Nights Pro screen shots.

Things to notice in the charts:

  • First Jupiter joins Venus and Mercury, then as it moves on, Venus, Mercury, and Mars form a trio.
  • Mercury never puts in a good appearance this month and it gets more difficult to see near the end of the month.
  • Jupiter does just the opposite, getting easier to see earlier in the morning as the month goes on.
  • On May 1 a slither of the waning crescent Moon is in the picture.
  • On May 29 the waning crescent Moon re-enters the tableau and will be present the rest of the month, though quite challenging on the last day. (The amount of Moon that is lit and its exact location will vary with your location.)

Notice the waning crescent Moon has entered the picture? It will be here three days, the last near Mercury.

Planet summary for May

Mercury – It is visible all month, but so close to the Sun and horizon you’ll need binoculars to spot it.

Venus – How can you miss it at magnitude -3.4?  Easy. It too is getting close to the Sun.  But look at the right time and you’ll see it and with the naked eye.

Mars – Very tiny and very dim right now because it’s about as far away from Earth as it can get and also is challenged by the pre-dawn twilight. But at least Jupiter will be of help early in the month in finding Mars.

Jupiter – Assuming you can find it, will guide you to Mars because Jupiter, though visible only during twilight, is comparatively bright.

Saturn – You can’t miss it – it’s the one planet high in the southeast and south in the evening – not morning – sky.  It is still visible in the west in the early morning hours. It sets as the pre-dawn planet show begins.

Uranus – A real challenge for binocular users.

Neptune – Even more of a challenge and as with Uranus binoculars are an absolute must.

Pluto -Hey, I mention it because it’s there – but this takes a fairly large telescope, a good chart, and a lot of patience. Since this post is aimed primarily at those using the naked eye and binoculars, I won’t mention it again – just kind of fun to know it’s out there with the rest of the gang in the pre-dawn sky even if its status has been demoted to dwarf planet.

Look North: Polaris gets two bright flankers in May!

Click for larger image. (Developed from Starry Nights Pro screen shot.)

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Is the North Star – Polaris – our brightest star? No! And it certainly won’t look that way this month as it shares the northern sky with two very bright stars. But, read on. Polaris is not nearly as dim as it looks!

If you have been learning your guidepost stars as they rise in the East, you won’t be surprised by the two bright stars which flank – and outshine – our pole star in May. To the northwest is Capella, a star we first met when it rose in the northeast in November. In May the northeast is dominated by a star that is almost Capella’s twin in brightness, Vega, a guidepost star we introduce in May. (See “Look East!” for more about Vega.) As a bonus we also have the twin guidepost stars, Castor and Pollux, coming into view high above Capella, as we face north. But let’s focus on Capella and Vega.

New star watchers frequently assume the North Star, Polaris, will be the brightest star in the sky. It isn’t even close! It is bright, but its fame comes because it’s very, very close to where the axis of the Earth points to the north celestial pole. So it serves anyone trying to find true north as a very good guide. But when it comes to brightness, it’s in the same league as the stars in the Big Dipper. Quite bright, but it can’t hold a candle to Capella and Vega. When you look at a list of the brightest stars, Vega is number 5 and Capella number 6. Polaris, our North Star, is number 48!

As simple as one, two, three!

That doesn’t mean Polaris is a slouch, though. First, in the eastern sky in May you meet Spica. (That’s on our chart for the east.) One distinction of Spica is that it’s as close to being magnitude 1 as any star gets. A distinction of Polaris is, as Spica defines magnitude 1, Polaris defines magnitude 2. (To be precise it’s magnitude 2.02.) Vega and Capella are extremely close to magnitude 0. Vega is 0.03 and Capella 0.08. Good luck on telling the difference! This month, if you look north 90 minutes after sunset, you may think Capella is a bit brighter actually – but if it appears that way it will be because it’s a bit higher in the sky and thus is not dimmed by having to fight its way through as much of our atmosphere as Vega is doing at the moment. So don’t try to split hairs. And yes, you’re right – they are NOT really as “simple as one, two, three” – on the magnitude scale they are as simple as zero, one, two – but that didn’t sound as good! (Vega and Capella are zero; Spica is magnitude one, and Polaris, magnitude two.)

So which is really the brightest star of these four? Are you ready for this? Polaris! That’s right – if you put all four stars at the same distance, Polaris would appear to be the brightest. Remember, that the lower the magnitude number, the brighter the star. In absolute magnitude, these four stars line up this way:

  • Polaris -3.4
  • Spica -3.2
  • Capella 0.1
  • Vega 0.3

And those absolute magnitudes also reflect their order in distance from us.

  • Polaris 433 light years
  • Spica 250 light years
  • Capella 45 light years
  • Vega 25 light years

So sometimes a star is very bright because it’s – well, very bright. But sometimes it only appears to be very bright because it is very close to us. If you put our closest star into this group, our Sun – remember, it is just 8 light minutes from us – in absolute magnitude it would be by far the dimmest of this group – absolute magnitude 4.9! So while Polaris doesn’t look all that bright, it really is a very bright star! Another way to think about this is if you move our Sun out to where Polaris is, it would be about magnitude 10. You would need a telescope to see it!

And here’s one more cool secret about Polaris. It has a companion that just happens to be quite dim – magnitude 9. It’s fun to see the two of them if you have a small telescope, though it’s not all that easy because Polaris is so much brighter than its companion. But if you get a chance to see Polaris and its companion in a telescope, remind yourself that the very faint companion is still a bit brighter than our Sun would look at this distance. This companion, known as Polaris B, was discovered in 1780 by William Herschel, and for many years Polaris was thought to be a binary star – that is, a system of two stars orbiting about a common center of gravity. But Polaris was holding one more surprise – it’s really a triple star. This has been known for some time, but no one could see the third star until they turned the Hubble Space telescope on it in 2006. That’s when NASA released the first image of this third companion. The accompanying press release explained it this way:

The top image shows Polaris and its faint companion that can be seen in any decent backyard telescope. The bottom image shows the second companion, Polaris Ab, which has only been seen by using the Hubble Space Telescope.

By stretching the capabilities of NASA’s Hubble Space Telescope to the limit, astronomers have photographed the close companion of Polaris for the first time. They presented their findings today in a press conference at the 207th meeting of the American Astronomical Society in Washington, D.C.

“The star we observed is so close to Polaris that we needed every available bit of Hubble’s resolution to see it,” said Smithsonian astronomer Nancy Evans (Harvard-Smithsonian Center for Astrophysics). The companion proved to be less than two-tenths of an arc second from Polaris — an incredibly tiny angle equivalent to the apparent diameter of a quarter located 19 miles away. At the system’s distance of 430 light years, that translates into a separation of about 2 billion miles.

“The brightness difference between the two stars made it even more difficult to resolve them,” stated Howard Bond of the Space Telescope Science Institute (STScI). Polaris is a supergiant more than two thousand times brighter than the Sun, while its companion is a main-sequence star. “With Hubble, we’ve pulled the North Star’s companion out of the shadows and into the spotlight.”

So as I said, Polaris is no slouch. It not only is a very bright star, but it also has two companions, and scientists are still studying it because it is unusual in other respects. We’ll talk about those other differences another month.

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