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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.

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.

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

 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.)

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 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.

Look East! Slide down to Spica in May 2011, then look back at Vega!

It’s a tad easier to find 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 2011 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. But sorting them out may prove a bit confusing. Don’t despair. 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, Spica. Saturn is between Arcturus and Spica, but quite a bit higher and almost the exact same brightness as Spica. 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 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 Arcturus, Spica, and Saturn form a nice triangle this spring. 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 monthSaturn 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 a good guide this month as to where the celestial equator is. Think of the celestial equator as a projection of the Earth’s equator onto the dome of the sky. It forms a great arc and as you stand, looking south, it passes across your sky from left to right – east to west. How high does it get? Subtract your latitude from 90 degrees and you’ll get the answer in degrees – for me it’s 48.5 degrees. But it’s easier these May nights to simply watch the path of Saturn, since it is less than two degrees south of the celestial equator. That means Saturn rises just a bit south of due east, sets a bit south of due west, and its path forms an arc that is a good approximation of the celestial equator. The Sun follows that same path when near the equinoxes in March and September. Arcturus will make a similar arc, but about 19 degrees north of the celestial equator, while Spica will be about 11 degrees south of it.

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. For more on star color see this little project. )

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! I can’t think of a better place to start  making the night sky your own.

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 the star. (For a 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)

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 faintest 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 Wikipeda 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 cannot 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.)

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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 2011 by the presence of  Saturn just a bit north of the ecliptic, as noted on our chart. Don’t confuse the ecliptic with the celestial equator, however. The celestial equator is a project of our equator onto the sky and is an imaginary line. The ecliptic marks the apparent path of the Sun in our sky and represents the plane of the solar system – that’s why the planets are always near it.  From mid-northern latitudes the ecliptic can go pretty far north or south – just think of how far south the Sun rises in winter and how far north it appears to rise in summer.  The celestial equator is always going to align with the due east and due west points on your horizon.

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, Regulus,  the Beehive, Procyon, Sirius, Pollux, Castor, and in the northwest near the horizon, Capella, and the Kite. If you look early in the month you may catch a glimpse of Sirius and Betelgeuse before they set.

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