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  • Rapt in Awe

    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 for May 2010: A good month to get to know the planets – especially Uranus!

Note: While many of the following events are visible throughout the world, the exact time and location in the sky can be dependent upon your latitude and longitude. Since I’m in the mid-northern latitudes (41.5N, 71.1W), specifics, where place-and-time-dependent, are calculated for this location.

   

Planets to scale - source unknown, but a very nice illustration! Click for larger image.

All  month – This a great month to meet planets – you’ll find they each have a distinctive appearance to the naked eye – and this is an especially good year to get out your binoculars and meet Uranus. A special window of opportunity opens in the morning starting about May 25, 2010.

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

 

But before delving into that exploration, just get out early on any May evening and you’ll find three bright planets waiting for you, and on certain nights, the Moon will be close to one or the other providing a sure guide to locating the planet. But even without the Moon, the easiest to spot is Venus. It will be low in the northwest, but only the Moon and Sun outshine it. Venus can be an “evening star,” as it is now, or a “morning star,” as it will be near the end of the year, but whichever it is there’s no star or planet that outshines it. So you’ll always know Venus by its brilliance.

A crescent Moon plays tag with Venus on May 15 and 16th.  Exactly how close it gets depends on where you are. For folks in southern Asia and northern Africa, the Moon will actually occult Venus – pass in front of it. Here in Westport, MA (41.5N,71.1W), it’s not nearly so dramatic, but still will make  a nice scene in the evening twilight. On the 15th the Moon is about six degrees below Venus, and on the next evening it’s about six degrees above it. (Remember, your fist held at arm’s length covers about 10 degrees.)

Mars is easy to spot this month for three reasons. First, it’s high in the southwest. Second, it has a distinctively reddish cast. And third, it’s moving between the Beehive – which we met in March – and Regulus, one of our bright guidepost stars, whipping along at the rate of about half a degree a day. That means each day it will cover a space against the background of fixed stars that is the size of the full Moon. To put this into perspective, Uranus takes about 44 days to cover the same distance! On May 19 the Moon will be about six degrees below Mars.

Finally, Saturn is shining at almost the same brightness as another nearby guidepost star, Spica. This is about as dim as Saturn gets and the reason, as backyard telescope users know, is that Saturn’s rings are titled almost edge-on to us. That means they just make thin spikes pointing out to either side of the planet when seen in a telescope – interesting, but not the beauty we’re used to. It also means that the planet and rings aren’t reflecting as much sunlight our way as they usually do and thus Saturn appears relatively dim – though still as bright as the 16th brightest star, Spica. Saturn is more subtle than Mars in coloration, but it always seems to have a soft yellow glow, and when I see a bright, yellowish “star” where no bright star belongs, I know it’s Saturn.

Well – I should modify that last statement a bit. When I see such a “star” near the ecliptic I know it’s Saturn. The ecliptic is the path of the Sun across our sky, and the planets appear within a wide band that stretches about one fist above or below the ecliptic. To get a sense of this band, let your eyes wander from Saturn to Mars to Venus. The arc you see connecting these planets pretty well defines the general area of the sky where you’ll always see the planets. Another way to think of this is the ecliptic is the plane of our solar system – the planets circle the sun in what amounts to a huge disc. And you can sense that as you look at them in the evening sky this May.

Of course the Moon appears in this same general band of sky and comes fairly close to the planets from our point of view. On May 22 the Moon will be about 8 degrees below Saturn. However, keep in mind that the Moon will be about 10 days old at that time and quite bright, so it will drown out most of the stars near it, though Saturn should be bright enough to still see easily.

And now, as promised, Uranus!

We’re missing Mercury this month. It puts in a very minor appearance in the morning sky late in the month and won’t be easy to see, but we do have Jupiter rising in the morning sky, and it is easily visible before dawn after mid-month in the east. It’s second in brightness only to Venus. What’s more, it’s going to be our guide for finding Uranus. The ancients were very familiar with the five “wandering stars” we just mentioned – Mercury, Venus, Mars, Jupiter and Saturn. They watched them regularly and knew well where to find them. So can you. But the ancients never saw Uranus, though it is just on the edge of naked eye visibility. I’ve never been able to see it except with binoculars or a telescope. And when you do find it with binoculars, it looks just like a faint star.

In fact, on March 13, 1781, the English astronomer William Herschell pointed one of his large telescopes toward some faint stars in the constellation of Gemini and suddenly discovered that one of them just didn’t look like a star.  In fact, as he increased magnification he saw it as a distinct disc and he was quite pleased at himself for having discovered – a comet! That’s right. At that time no one was thinking much about more planets.  Comets were all the rage, though. In fact, when Herschell checked four days later, his discovery had changed position slightly and he took this as proof that it was a comet.

But it wasn’t. Herschell’s new comet never developed a tail.  It was soon determined that Herschell had not only discovered a new planet, but in doing so he had doubled the size of the known solar system. Uranus, while big enough to swallow 64 Earths, was in fact more than twice as far from the Sun than Saturn, which at that time marked the end of the known solar system.  And that great distance is, of course, why Uranus appears so small and so dim to us. Even with a good-sized amateur telescope you can just tell you are looking at a planet and not a star. And while it has rings, as Saturn does, they’re much too faint to see.

Let Jupiter help you out!

But this year Uranus will be simple for you to find if you have binoculars. All you’ll have to do is find Jupiter, then use your binoculars and the appropriate chart below to determine which “star” is really Herschell’s new planet. You can begin this process about May 25, and the opportunity will be there through June. Yes, that means getting out there about 3:30-4 am and that may not fit your schedule. If so, don’t despair. Jupiter and Uranus will be in the early evening sky in the fall and in winter as well, so there will be two other “windows” when locating Uranus with binoculars will be easy this year. Both of these will allow viewing in the evening hours that most people keep.  But do take advantage of one of these. Otherwise you have to wait about 26 years for another chance! (Of course you can find Uranus any year – but it’s much easier to do so when it is right next to a bright planet like Jupiter.)

Here are charts that you can use in May and June. They  show the position of Uranus and Jupiter  about 3:30 am on May 25, June 6, and June 30, 2010.  Study each chart and you will see that in the new few weeks Uranus will appear to move to the right while Jupiter moves to the left.  They will be closest together on June 8 but should still fit in the same binocular field at the end of the month. (The circle represents a typical binocular field ifor 10X50 binoculars.  Depending on exactly what you’re using, your field of view may be larger.)  Do enlarge the image by clicking on it and do note that you can download a printer-friendly version of each chart using the links below.

To make any sense of this you really have to click the image and look at the larger version. You can then select one or more of the panels from the list below to get a printer-friendly PDF file that you can use outside. (Charts prepared form Starry Nights Pro screen shots.)

For a printer-friendly version of the appropriate chart for on or near May 25, 2010, click here.

For a printer-friendly version of the appropriate chart for on or near June 6, 2010, click here.

For a printer-friendly version of the appropriate chart for on or near June 30, 2010, click here.

What’s in a name?

And since we’ll be talking about Urnaus a lot this year, let’s get the silliness surrounding its name out of our heads right now. The best way to pronounce the name Uranus is “YOOR-ah-nuss”, not “your anus” or “urine us.” Remember that – or risk having your audiance – especially if they’re shcool children – distracted by a bad case of the giggles!

Sometimes I wish we had listened to Herschell. When he discovered this planet he named his discovery “Georgium Sidus” which means the Georgian Planet in honor of King George III of England. I doubt that this idea went over well in America at that time – in March 1981, just before Herschell made his discovery, the colonies officially ratified the Articles of Confederation and Perpetual Union – essentially our first Constitution. Of course Herschell’s wise choice of this name led to him getting a lifelong stipend!   But the name didn’t stick and astronomers applied others and it was Bode of Germany who suggested Uranus, the ancient Greek deity of the heavens. It took another 50 years or so for that to catch on, but now it’s not about to change.

Night-by-night summary

All month – Look for the bright planets along the ecliptic from east to west – Saturn, Mars, and Venus.

May 4-7 – Don’t get excited – this is not a big event – but I would feel remiss if I didn’t mention the Delta Aquarid meteor shower. In the early morning hours, northern hemisphere observers may see a few bright meteors associated with this shower, but this event is much better in the southern hemisphere, and this year no matter where you observe a waning Moon approaching last quarter will provide unwelcome competition, brightening the sky and drowning out all but the brighter meteors. ould be good on any morn

May 6 – Last quarter Moon lights up the  morning sky.

May 13 – New Moon.

May 15, 16 – A crescent Moon plays tag with Venus.  Exactly how close it gets depends on where you are. For folks in southern Asia and northern Africa, the Moon will actually occult Venus. Here in Westport, MA (41.5N,71.1W),  it’s not nearly so dramatic but still will make  a nice scene in the evening twilight. On the 15th the Moon is about six degrees below Venus and on the next evening it’s about six degrees above it.

May 19 – The Moon is about six degrees below Mars.

May 20 – First quarter Moon.

May 22 – A 10-day-old Moon is about eight degrees below Saturn.

May 25 – Good day to start your quest for Uranus with Jupiter as your guide in the early morning sky.

May 27 – Full Moon.

Note: There is one category of special events worth checking on that is not listed here because the events very specific to where you live and when you observe. These are events involving man-made objects in space – the passages of the International Space Station, Iridium flares, and other bright satellites. There are two excellent  sources for such events. I urge you to check both, see how they differ, and then make your own decision as to what works best for you.
  • The first is provided by Spaceweather, and you’ll find it here.
  • The second is the Heavens Above site, and while this requires you to register, the process is painless and free and the result is a lot of information that is specific to your location. Once registered and logged in, study the menu – there’s a wealth of information on satellites and many other astronomical objects.

Look East! Slide down to Spica in May, 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 2010 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 th e 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! 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 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 just three degrees north of the celestial equator. That means Saturn rises just a bit north of due east, sets a bit north 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. The three stars of Orion’s belt also follow the same general path.

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.

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)

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 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 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 2010 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, Regulus, Mars, 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: In May 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 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 released 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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