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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.

Look North in November into the Dragon’s Lair

Click image for larger view. Remember: This chart is for about 90 minutes after sunset.  With each passing hour these stars will rotate counter clockwise around the Polaris, the North Star.  So Vega will appear to get lower as the night goes on and Capella will be getting higher. (Prepared from Starry Nights Pro screen shot.) 

Click here for a printer-friendly version of the above chart.

Our north sky map this month is covering a slightly larger area than normal because I want to capture the relationship between Vega and Capella – two of our northernmost guidepost stars – that anchor the north sky in November. Think of them as two cornerstones and a line drawn between them will go quite close to the North Star, Polaris. What’s more, Vega will help us find the head of Draco the Dragon.

Draco is one of the north sky’s more charming constellations, for its long, slithery form does call to mind a dragon. It’s quite easy to pick out, really, but you do need dark skies with little light pollution. Start by locating Vega. The four stars that mark the head of Draco – one is quite faint – will be found roughly halfway between Vega and the two bright stars that mark the end of the cup of the Little Dipper. Having located the head, you really need a chart handy to find the rest of this long, twisting, dragon body – but it is pretty easy, and once you identify it, you won’t forget it.

Draco also harbors a special treat for binocular and small telescope users. That faint star (Nu) that marks one corner of the Dragon’s head? It’s really two, perfectly matched, 4.9 magnitude stars that are far enough apart so they can be split with binoculars – assuming you have good eyes and a really steady hand. In a small telescope they are absolutely delightful and earn their nickname of Dragon’s Eyes. ( There are actually three neat double stars in this region that are a delight for the telescope user. I’ve written about them in the double star observing blog I share with my friend John Nanson.)

Meanwhile, to the east we have a bright half circle of asterisms we’ve been talking about in the previous months. Start with Capella and move on up to the “Bow” of Perseus and from there higher still to the “W” of Cassiopeia. Directly above the Pole you’ll find the “Home Plate” of Cepheus pointing down towards Polaris.

Look North in October 2014 – and find a really bright star!


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

For a printer-friendly version of this chart, click here.

When I say “really bright,” I mean Capella – and I say it because so many folks assume, quite understandably, that the North Star will be the brightest in that section of the sky. It isn’t.

Capella is one of our brightest stars, and you may catch it this month just peeping up over the northeastern horizon about an hour and a half after sunset. And it is brilliant!  When you see Capella,  compare it with the North Star  and you will get a good idea of what the word magnitude means. There are a solid two magnitudes difference between the two – or if you want to get technical, Capella is magnitude 0 and Polaris is magnitude 2.

Yes, the magnitude system goes backwards – the lower the number, the brighter the star. Each magnitude difference represents a change of about 2.5 times in brightness. So a zero magnitude star is 2.5 times as bright as a first magnitude star – and 2.5 x 2.5, or 6.25 times as bright as Polaris, a second magnitude star. And while we’re on this subject, the faintest star in the Little Dipper – it’s over in one corner of the cup – is just about magnitude five. That means Capella is 100 times as bright as that star. (OK – if you actually do the math it doesn’t come out because I rounded off the difference – it’s really 2.512 for those wanting more precision.)

In fact, there is another interesting way to look at that star – at magnitude 4.9 it is almost exactly what our Sun would look like if it were placed just 32.5 light years away. At that distance our sun would be magnitude 4.8 – and that distance is the distance we use to compare stars. That is, to get an “absolute magnitude” for them so we can compare apples with apples,  we ask ourselves how bright a star would be if it were 32.5 light years from us.

And while we’re on the subject of magnitude, the Little Dipper does give us a great range. Polaris, as we said, is magnitude 2. The other bright star in the Little Dipper is magnitude 2 also – it’s at the end of the cup away from Polaris. Sharing that end is a magnitude 3 star, and these two are known as the “Guardians of the Pole” as they are prominent, close, and like other stars, circle around the pole  every 24 hours. Most of the other stars in the Little Dipper are magnitude 4, with the one star in the far corner of the cup being magnitude 5, as noted – well, actually 4.9. There’s a chart with these magnitudes in this post. Many people who live in light-polluted areas can see only three stars in the Little Dipper – Polaris and the two Guardians of the Pole.

How faint a star can you see? Depends upon your eye sight, the light pollution in your area, the transparency of the skies on any given night, how high the star is in the sky, and, of course, your vision and dark adaption. But as a general rule of thumb magnitude 6 has been accepted as the typical naked eye limit. However, if you live in a typically light polluted suburb you may see only to 4, or worse yet, magnitude 3. And observers on mountain tops with really clear skies reliably report seeing stars as faint as magnitude 8. All of this is with the naked eye. Add ordinary binoculars and you will certainly add three to five magnitudes to the faintest star you can see. In fact, you take a huge jump in the number of stars seen just by using binoculars with 50mm objective lenses. That’s why many amateur astronomers with fine telescopes also are likely to have a pair of 10X50 binoculars that they keep handy. I always did, but more recently I stumbled upon some very inexpensive Celestron 15X70 binoculars that I love for quick peaks, though they are two powerful and large to hold steady for serious observing.

For more serious work I now use relatively expensive 10X30 image stabilized binoculars. Yes, the 30mm means they do not gather nearly as much light as the 50mm standards – but the image stabilization means they take better advantage of the light they do gather. They’re also more compact and light, so I  don’t mind carrying them for several hours.

Capella will be a “look east” guide star next month, but you can get to know it this month as you look north. And if you live in mid-northern latitudes, it will become a most familiar site. In fact, where I live – about latitude 42°N – it is in the night sky at some time every night of the year. This is because it is so far north that as it circles Polaris, it only dips below the horizon for a few hours at a time.

Look North in June 2014! See the ‘North Sky Triangle’ !

Click to enlarge. (Prepared from Starry Nights Pro screenshot.)

For a printer-friendly version of this chart, click here.

Yep, that’s Deneb, the guide star that is the subject of our “Look East” Post for June, gracing our “Look North” chart as well. In fact, besides Polaris we have three key guide stars in our northern sky every June, each of which is noted for, among other things, just how far north it is.

Of the three, Capella may be the hardest to find, for it is very near the horizon in the northwest around sunset. But if you have a clear horizon in that direction, you should still pick it up, especially at the start of the month. More prominent, however, are Deneb and Vega. These stars play the key role in one of the best known sky triangles – the Summer Triangle, but that triangle becomes easier to see next month and it will be in the eastern sky. For June it is fun to link Deneb and Vega with Polaris in what we’ll call the North Sky Triangle – and the linkage has some special meaning.

We just happen to be lucky to be living in an era when we have a bright star near the North Celestial Pole – Polaris. There’s no such bright star near the South Celestial Pole, and in other eras there is none near the North Pole either. But in the distant past – and in the distant future – Deneb actually will be the bright star nearest the pole – not as near as Polaris, but still a good general guide to it.

gyroscope precessionThat’s because the Earth wobbles as it spins on its axis in much the same way as a spinning top does. So the axis of the Earth doesn’t always point to the same place. It slowly makes a great circle around the northern sky, taking roughly 25,000 years to complete. Right now our axis is pointing to within a degree of Polaris. Not precise, but good enough so it is a ready indicator of true north. A mere 18,000 years ago Deneb was within 7 degrees of the pole and will be again around the year 9800!

This wobbling of the pole is really kind of mind boggling. I look at Polaris now, and it’s a bit short of 42 degrees above my northern horizon. But in a mere 14,000 years, Polaris will be almost straight over my head, and guess what will be the pole star then? Not Deneb, but its brighter – in our skies – companion, Vega. Of course none of us is likely to witness that event, but it’s still food for thought and gives us a sense of the majestic rhythms and time frame of the heavens.

And speaking of that time frame, as I write this it occurs to me that 14,000 years really feels like a very long time from now – while the 10-million-year age of Deneb doesn’t seem that long – and it isn’t, astronomically speaking. I’m not talking now about what your mind tells you about those numbers. I’m talking about your emotional reaction to them. I wonder if it’s similar to mine? This isn’t idle speculation. It’s central to our appreciating what we are seeing. But I think 14,000 sounds like a long time because it’s a number that fits into our day-to-day experience. Huge, but we can easily imagine 1,000 of something.  So imagining 14,000 of something comes easily to us. But few of us have any experience with one million. It would take about 11 days to count one million seconds and no one in his right mind is about to try it. So when we speak of the 10-million-year age of Deneb, or the five-billion-year age of the Sun, the numbers lose their emotional impact because they don’t relate easily to our experience. But 14,000 – well, we know, in an emotional sense, just how long that is!

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 in February 2014: Two dogs – plus Jupiter – rising in a star-spangled spectacular – the Winter Hexagon

We have two “dog stars” on the southeastern horizon early on February evenings  – Sirius and Procyon – and  both are part of what is certainly the brightest, star-spangled  section of our northern night sky – the Winter Hexagon.  Adding to this annual dazzle in 2014 – and brighter than any star – is the “wandering star” (i.e., planet) Jupiter, smack in the middle of the Gemini twins -about halfway between their heads and feet.

Here’s how the Winter Hexagon looked to the camera of Jimmy Westlake who took this gorgeous shot as it loomed over Stagecoach, Colorado, USA.  You may not see the faint band of the Milky Way shown here if you live in a light polluted region, but you certainly should be able to pick out the bright stars that outline the Hexagon, as well as the Pleiades star cluster visible near the top and just right of center.

Click on image for much larger view! (Copyright © 2007-2011 JRWjr Astrophotography. All rights reserved.)

Look carefully at that photo, then compare it with this star chart, which is what we see from mid-northern latitudes as we look southeast early on a February evening.

Click image for much larger version. To get the full beauty of this section of sky find an area with a clear horizon to the southeast and go out on a February evening a couple of hours after sunset. The chart shows what you'll see. The link below provides a small black-on-white version you can print and take into the field. (Prepared from a Stellarium screen shot.)

Click image for much larger version. To get the full beauty of this section of sky find an area with a clear horizon to the southeast and go out on a February evening a couple of hours after sunset. The chart shows what you’ll see. The link below provides a small black-on-white version you can print and take into the field. (Prepared from a Stellarium screen shot.)

For a printer-friendly version of this chart, click here.

People in the north tend to think that the stars are brighter in winter because the air is so cool and crisp. That certainly could be a factor. But the simple fact is our winter sky is dominated by a whole lot of very bright stars. In fact, visible from earth are 22 stars of first magnitude. Sixteen  of these are visible from the Northern Hemisphere, and half of these are visible in the area of the Winter Hexagon on a February evening. That means nearly all these bright stars are jammed into a space taking up less than one-quarter of the February night sky – which is  just one-eighth of the total night sky we can see through the year! In other words, if bright stars like these were scattered throughout the night sky evenly there would be 64 first magnitude stars instead of just 22. Add to that the seven bright stars of the Big Dipper being dragged up the northeastern sky by the Great Bear on a February evening, and it is no wonder that in the dead of a northern winter our skies offer a lively, colorful, star-spangled spectacular.

The Hexagon alone contains seven of the first magnitude stars in our sky and an eighth that is the brightest second magnitude star we see. This one – Castor – just misses being first magnitude by a hair.  And nearby is Adhara, a star that sits right on the border between second and first magnitude; plus Regulus, another first magnitude star, is rising low in the east. Whew! That’s a lot. Let’s review.  Going  counterclockwise and starting at the bottom, the Hexagon’s corners are marked by:

  • Sirius, the brightest, and at about eight light years one of the closest, stars in our sky – except the Sun, of course.
  • Rigel, the blue giant that marks one of Orion’s feet.
  • Aldebaran, the brilliant orange star that is the eye of Taurus the Bull and dominates the nearest open star cluster, the Hyades.
  • Capella, now high overhead, is really a complex of four stars that we see as one.
  • Castor and Pollux, the twins, one of which (Pollux) is first magnitude, while Castor is the brightest second magnitude star we see.
  • Procyon, the “Little Dog” star, which is dim only in comparison to Sirius, the “Big Dog.”

And . . .

  • Inside the Hexagon is another first magnitude star, Betelgeuse, the red giant that marks Orion’s shoulder, not to mention the three bright stars of Orion’s Belt – all second magnitude.
  • Regulus, the “Little King,” is a first magnitude star that is rising in the east and bringing us the familiar sickle of bright stars that mark the head of the lion. We’ll study it closely next month.
  • Adhara is the western-most star of the distinctive small triangle of stars beneath Sirius. At magnitude 1.5 I call it a first magnitude star, but others consider this second magnitude. So depending on how you count Adhara there are either 21 or 22 first magnitude stars.

Before leaving the Winter Hexagon, I must stress that  this is not simply a northern hemisphere show – if you live  in Sydney, Australia, you could just rename this the “Summer Hexagon.” I see these stars in the southeast – my friends in Sydney see them in the northeast of their sky – and, of course, since they’re “standing on their heads,” they see them a bit differently – something like this!

The “Winter Hexagon” becomes the “Summer Hexagon” in the Southern Hemisphere, but contains all the same bright stars. (Chart prepared from Starry Nights Pro screen shot.)

February Guidepost Stars

Of the stars mentioned so far, the two dog stars, Sirius and Procyon, plus the fence sitter, Adhara, are the guidepost stars to learn this month. They are the ones you can spot near the southeastern horizon, coming into view about 45 minutes to an hour after sunset. (We’ll have more to say about Regulus next month, and the other stars mentioned we’ve met in previous months.) To see the February guidepost stars – and the asterism of the Virgins –  look low in the southeast about 45 minutes to an hour after sunset.  Here’s what you should see.

Click image for larger version. This chart shows the three guidepost stars for February as they appear about an hour after sunset in the southeast. Sirius is the brightest star we see and Procyon is not far behind, but Adhara is not much brighter than its companions, which form a distinctive, small triangle the ancient Arabs knew simply as “the Virgins.” (Prepared from Starry Nights Pro screen shot.)

For a printer-friendly version of this chart, click here.

Procyon, the seventh brightest star we see, is first up in our sky, and thus the highest, of these three. To the southeast and a tad lower is brilliant Sirius, brightest star in our sky, and next to the North Star, Polaris, probably the best known star in the world. Adhara is the brightest star in the “Virgins,” a simple,  distinctive  triangle asterism. But, of course, Sirius is dominant – far brighter than any other star we see in our night sky. I always think of Sirius as the eye of the great dog and as he sits, the triangle seems to be his rear haunches. From our perspective Adhara may be just another bright star, but of these three it is really the brightest by far – it’s just much farther away than the other two.  If we compared them side by side we would find that Procyon shines with the light of seven Suns, Sirius 23, and Adhara has a luminosity to the eye of 3,700 Suns! Now that’s bright.  And in another way, Adhara reveals our human bias, for if we had ultraviolet vision Adhara would be the brightest star in our sky, not Sirius. But again – that’s not the way we see it. From our perspective, Sirius and Procyon are very bright because they are very close to Earth. Sirius, at a little more than eight light years is the closest star that we in the mid-northern latitudes see in our night sky. Procyon, at about 11 light years, is fourteenth on the list of nearest stars.  Most of the stars that are nearer than Procyon are also much fainter – in fact, too faint to see with the naked eye. If we count just those stars bright enough to see with the naked eye, Procyon is the sixth closest and Sirius is the second closest.  (The closest star, Alpha Centauri, is visible only to those in, or near, the Southern Hemisphere.) But Adhara? Adhara is 405  light years away – about the same distance as the North Star, Polaris. Sirius will frequently seem to be changing colors, but that’s just the effect of our atmosphere. Just as our atmosphere makes our Sun look red when it is rising or setting, it makes any bright star near the horizon appear to dance and change colors rapidly.

The Big Dog as Johannes Bayer depicted him in 1603. (Image courtesy of Linda Hall library of Science, Engineering and Technology.)
The Little Dog as shown in the 1603 Uranometria chart. (Image courtesy of Linda Hall library of Science, Engineering and Technology.)

Sirius is known as a “dog star” because it is the brightest star of the classic constellation, Canis Major – the Big Dog. Procyon is the brightest star in the constellation Canis Minor, the Little Dog. When you look at these constellations as depicted in early star charts, it’s hard to see how connecting the dots makes the stars take the forms the constellation’s name implies, but the images are still useful memory joggers.

Modern science, though, gives us even more reason to remember these two stars, or rather the faint companion stars that orbit them. These are designated Procyon B and Sirius B and they defy our ability to even imagine because there’s just nothing in our down-to-earth experiences that compare with these tiny stars.  One of these “pups”  – the one belonging to Procyon – is impossible to see with a backyard telescope and the other an extreme challenge.  The reason is they are quite dim and being very close to the bright stars, get lost in the glare.

But the mystery of these two fainter stars is that they are both white, indicating they are among the hottest of stars. So how could something be that hot, that close to us, and yet so dim? And the answer is more mind-boggling than the question – they are both white dwarfs, and white dwarfs are a class of stars far denser than anything we encounter on Earth. Now I always find talk of the density of stars counter-intuitive because it gets drilled into our heads that stars are gas and the gas we encounter in our daily lives is anything but dense!  In fact, it’s quite – well – gaseous!  To appreciate this, let’s take a close look at our own Sun.

Click image for larger view.Sirius – with Sirius B at lower left.  Credit: NASA, H.E. Bond and E. Nelan (Space Telescope Science Institute, Baltimore, Md.); M. Barstow and M. Burleigh (University of Leicester, U.K.); and J.B. Holberg (University of Arizona)

The Sun is a ball of gas which reaches densities that near the center are sixteen times that of lead!  That alone should stretch your mind. But now imagine the white dwarf. The stuff that makes up a white dwarf is about one million times denser than the stuff in the Sun.

Jim Kaler writes that if you had a billiard ball made up of the stuff of one of these white dwarfs it would weigh about 70 tons – roughly the weight of an M1 Abrams tank. (Think of what that would do to your pool table, not to mention your foot if it fell on it!)

We know this because we can calculate the mass of the stars by their orbit around their bigger, brighter companions. The result is, we end up with a mass roughly that of the Sun but a size roughly that of the Earth. You can fit one million Earths – and therefore one million white dwarfs – inside the Sun. (See why a white dwarf is one million times as dense as the Sun?)

How do you take all that mass and squeeze it down to such a small size? The physics of how that’s done goes way beyond me, but if you want to put a name to it, a white dwarf consists of “degenerate matter.” Unlike other stars, white dwarfs no longer burn with nuclear fires. In fact, they are no longer burning at all. They are the dying embers of stars – and in the case of the “pups,” the embers are being seen while still white hot. But they will eventually cool.

The name white dwarfs is given to this class of stars, but in truth not all white dwarfs are white – some can even be red. To make sense of this contradiction of terms, just think about an ordinary dying ember and how its color will change as it cools. So it is with these dying stars. Unable to generate any heat, what they radiate they lose.

This is also the ultimate fate scientists expect for our Sun.  As it eventually exhausts its nuclear energy, it will turn into a bloated red giant like Betelgeuse in Orion.  Later still it will blow off its outer shell of gases, turning into a planetary nebula, such as the Ring Nebula (M57) in Lyra.  And at the core of that nebula will be the dying ember we know as a white dwarf.

I’ve never seen the white dwarf that revolves around Sirius, but perhaps this season I will. Orbits are not circles, but ellipses. This means that sometimes there’s more distance between Sirius and its “pup” than at other times – and we happen to be in a period of several years when that distance will be growing, and so it will become easier to see the pup in a good, backyard telescope. (Sirius B completes an orbit around Sirius A in 50.2 years. Procyon B, while visible to professionals, is just simply too difficult a target for most backyard telescopes.) I also plan to take a close look at Adhara with a telescope, for it has a 7.5 magnitude companion just 7 arcseconds away. This should be a challenge – because of the difference in brightness of the two –  but not nearly the challenge that seeing the companion of Sirius is. For those with binoculars and small telescopes, some of the most fascinating objects are in this general area of sky, near, or inside the Winter Hexagon, including the Pleiades, the great Orion Nebula, and the spectacular telescopic open clusters in Gemini and Auriga, M35, M36, M37, and M38. All that star light certainly can make for bright nights during the dark  of a northern winter.

Vital Stats for the Guidepost Stars

For Procyon:

  • Brilliance: Magnitude 0.38, the 7th brightest star in our sky. Shines with the luminosity of about 7 Suns.
  • Distance: 11.4 light years
  • Spectral Type: F
  • Position: 07h:39m:18s, +5°:13′:29″
  • Procyon B is magnitude 10.7 and orbits Procyon in 40.8 years.  It can be as close as 9 AU to Procyon (1 AU is the distance between the Earth and Sun), or as far as  21 AU.

For Sirius:

  • Brilliance: Magnitude -1.5,  the brightest star in our sky.  Shines with the luminosity of about 23 Suns.
  • Distance: 8.6 light years
  • Spectral Type: A
  • Position: 06h:45m:09s, -16°:42′:58″
  • Sirius B is magnitude 8.3 and orbits Sirius in 50.2 years. It can be as close as 8.1 AU to Sirius, or as far as 31.5 AU. (It will reach this greatest separation in 2019.)

For Adhara:

  • Brilliance: Magnitude 1.5, it has a luminosity to the eye of 3500 times that of the Sun! (In other words, much brighter, really, than Procyon or Sirius.)
  • Distance: 405 light years
  • Spectral Type: B2
  • Position: 06h:59m, -28°:59′:18″

Look North in November 2013 into the Dragon’s Lair

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

Click here for a printer-friendly version of the above chart.

Our north sky map this month is covering a slightly larger area than normal because I want to capture the relationship between Vega and Capella – two of our northernmost guidepost stars – that anchor the north sky in November. Think of them as two cornerstones and a line drawn between them will go quite close to the North Star, Polaris. What’s more, Vega will help us find the head of Draco the Dragon.

Draco is one of the north sky’s more charming constellations, for its long, slithery form does call to mind a dragon. It’s quite easy to pick out, really, but you do need dark skies with little light pollution. Start by locating Vega. The four stars that mark the head of Draco – one is quite faint – will be found roughly halfway between Vega and the two bright stars that mark the end of the cup of the Little Dipper. Having located the head, you really need a chart handy to find the rest of this long, twisting, dragon body – but it is pretty easy, and once you identify it, you won’t forget it.

Draco also harbors a special treat for binocular and small telescope users. That faint star (Nu) that marks one corner of the Dragon’s head? It’s really two, perfectly matched, 4.9 magnitude stars that are far enough apart so they can be split with binoculars – assuming you have good eyes and a really steady hand. In a small telescope they are absolutely delightful and earn their nickname of Dragon’s Eyes. ( There are actually three neat double stars in this region that are a delight for the telescope user. I’ve written about them in the double star observing blog I share with my friend John Nanson.)

Meanwhile, to the east we have a bright half circle of asterisms we’ve been talking about in the previous months. Start with Capella and move on up to the “Bow” of Perseus and from there higher still to the “W” of Cassiopeia. Directly above the Pole you’ll find the “Home Plate” of Cepheus pointing down towards Polaris.

Look east in November 2013 for the “Eye of Sauron” star and its “zombie” planet!

November brings us our southernmost – and northernmost – guidepost stars, Fomalhaut and Capella. And  still a puzzle is the “Zombie planet,”  Fomalhaut b,  described by NASA last year in a Halloween video.  But first, the normal.

The positions of Capella and Fomalhaut in the sky mean that for Northern Hemisphere observers Fomalhaut is the guidepost star we see for the shortest amount of time – and Capella is the one we see the longest.

In fact, for many, Capella is visible during some hour every night of the year – and for those north of latitude 45 degrees, it is circumpolar – that is, it never sets. But lonely – and freshly fascinating – Fomalhaut just puts in a relatively brief appearance low to the south.

From NASA:”This image, taken with the Advanced Camera for Surveys aboard NASA’s Hubble Space Telescope, shows a newly discovered planet, Fomalhaut b, orbiting its parent star, Fomalhaut. The small white box at lower right pinpoints the planet’s location. Fomalhaut b has carved a path along the inner edge of a vast, dusty debris ring encircling Fomalhaut that is 21.5 billion miles across. Fomalhaut b lies 1.8 billion miles inside the ring’s inner edge and orbits 10.7 billion miles from its star.” Click image for larger version.

Fomalhaut is “lonely” because there are few bright stars in its vicinity. It is “freshly fascinating” because early in this century the Hubble Space Telescope got a fantastic picture of a disc of “debris” surrounding it, showing this young star to be in the throes of forming planets. Then in 2008 scientists announced they had actually found a planet circling Fomalhaut (see photo above), the first planet outside our Solar System to be seen with visible light. Cool! Add to this the fact that the Hubble photograph of Fomalhaut could be easily mistaken for the Eye of Sauron, and for fans of the Lord of the Rings movie triology, Fomalhaut becomes especially memorable. (For more on the “Eye of Sauron” go here.)

Why NASA calls it a “Zombie Planet”

More recent information doesn’t completely clear up the mystery – actually it gets weirder –  but they do seem pretty sure the planet is real.

Vital stats for Fomalhaut (FO-mal-ought)

• Brilliance: Magnitude 1.16; its luminosity is the equal of 16 Suns.
• Distance: 25 light years
• Spectral Types: A3V
• Position: 22:57:39, -29:37:20°

After reading this description, click on the chart for a larger version. About an hour after sunset, November evenings offer us an eastern sky filled with a host of asterisms both large and small. A good starting point for the naked eye is the Great Square of Pegasus. From one corner of it you can find Andromeda’s Couch which ties into what I call the “Demon’s Triangle” because it is anchored by the eclipsing variable, Algol – the “Demon Star.” The “W” of Cassiopeia should be obvious – and there are three asterisms shown that are best seen with binoculars. The “Hockey Stick” and “Water Jug” should fit in a low power binocular field, while only half of the “Circlet” will fit. Capella anchors our chart to the north, with Fomalhaut to the south. I included Deneb Kaitos because while it is a little dimmer than Fomalhaut, it could be mistaken for it. (Prepared from Starry Nights Pro screenshot.)

Click here to download a printer friendly version of the above chart.

Finding Fomalhaut

As always, it’s easiest if you start looking in the east 45 minutes to an hour after sunset when in the twilight only the brightest stars are visible as shown on our chart. Fomalhaut is the brightest star south of southeast and about a fist and a half above the horizon 45 minutes after sunset. Trailing well behind Fomalhaut – to the east – and lower still is a second magnitude star (same brightness as the North Star) called Deneb Kaitos. Don’t mistake it for Fomalhaut.

If you have learned the Great Square – see this post – then the two stars that form the western edge of that square can be used, as pointer stars. Drawing an arrow through those two stars leads you to Fomalhaut. You could also wait until a couple of hours after sunset when you would find Fomalhaut very close to due south. Even then, from my latitude of 41.5° N it is not quite two fists (19°) above the southern horizon.

Ahhh Capella!

Capella is distinctive because it’s not “a” star – it’s two! But these two, bright, yellow suns are so close together that you’ll always see them as one, even if you use a large telescope. Together they make a star that rivals Vega and Altair, now well into our western sky, in brightness. (See Summer Triangle chart here.) In fact Capella is the third brightest star in the Northern Hemisphere – but that’s a tad deceptive because it doesn’t count Sirius – the brightest star that most Northern Hemisphere observers can see, although technically Sirius is in the Southern Celestial Hemisphere, since it is below the celestial equator. But you don’t have to worry about such technicalities to enjoy a view of Capella. Just look near the horizon to the northeast. You will need a very clear horizon, however, especially at the start of the month because then Capella will not even be one fist above the horizon.

Just as Fomalhaut is a bit south of southeast, Capella is a bit north of northeast.

It’s easiest to find Capella if you start 45 minutes to an hour after sunset. Choose a spot with a clear horizon to the northeast and watch for a bright star to appear very near the horizon. Like all bright stars near the horizon, Capella will twinkle and flash in different colors because you are seeing it through a lot of atmosphere. It won’t show its soft, golden hue until it is much higher in the sky. Even a veteran skywatcher can be fooled by this. Recently my wife was looking to the northeast on a fall evening and saw what she thought was Capella. But it was so bright and blinking red and green so distinctly, that she changed her mind and decided it was an airplane! (There’s an airport off in that general direction.) When after a minute or so it hadn’t moved, she knew her first thought was correct – but boy it made a convincing airplane!

For me, Capella marks a graceful arc of bright stars and asterisms that circle the north celestial pole. If you have been following these directions for a few months, look at Capella, the “Bow” of Perseus, and the “W” of Cassiopeia to see what I mean. Watching these move in the course of a single night – or from month to month – always gives me a real sense of how, from our vantage point, all the stars appear to circle Polaris.

As mentioned, Capella is really a complex multiple star. Its two main components are both yellow giants dubbed Aa and Ab, but there are two more stars in this family. However, they are a pair of red dwarfs only visible in a telescope and are so far away from the two bright stars that they take more than 1,000 years to complete an orbit. The two bright stars orbit in just 104 days. James B. Kaler, in his book The Hundred Greatest Stars, says this about the Capella twins:

These two magnificent giants are separated by about the distance between Venus and the Sun. A resident on a ‘Jupiter’ ten times further out would see two ‘Suns’ about half a degree across (similar to the Sun in our own sky), separated at maximum by some 6 degrees, one setting right behind the other.
So when you find Capella, pause – picture yourself on the Jupiter-like planet with these twin yellow Suns in your sky!

Vital stats for Capella (kah-PEL-ah)

• Brilliance: Magnitude .08; its luminosity is the equal of 16 Suns.
• Distance: 42 light years
• Spectral Types: G8/G0
• Position: 05:16:41, +45:59:53

In this month’s chart I identify three relatively dim asterisms as good objects for your binoculars – there’s also the magnificent Andromeda Galaxy barely visible to the naked eye if you have very dark skies, but certainly a small blurry patch in binoculars. The arrows on the chart show two paths to tracking it down by star hopping. Found it? Pat yourself on the back. You are looking at about 300 billion stars and you are looking back in time about 2.5 million years!

The “Water Jug” of Aquarius is a nice binocular object. To me it looks just like a three-bladed airplane propeller.  The “Circlet” is part of Pisces and while quite faint, is easy to trace out in binoculars, though you will have to scan about a bit to see it all. It doesn’t fit in a single field of view – at least in most binoculars.

What I dub the “Hockey Stick” are the three brightest stars of Aries, the Ram. The faintest of these is an easy and beautiful double – a nearly perfectly matched pair if you have small telescope, point it at them and enjoy.

Still with us!

Other bright guide stars and asterisms introduced in previous months that are still readily seen include the Summer Triangle of Altair, Deneb, and Vega, which is high over head and crossing into the western sky. Arcturus is just above the horizon in the west, the Big Dipper just west of north and hugging the horizon, and the Teapot is diving into the ground in the southwest. And, of course, we have the “Bow” of Perseus with “Algol” the “Demon” star, the “W” of Cassiopeia, the “home plate” of Cepheus, Andromeda’s Couch, and the Great Square.

Look North in October 2013 – and find a really bright star!


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

For a printer-friendly version of this chart, click here.

When I say “really bright,” I mean Capella – and I say it because so many folks assume, quite understandably, that the North Star will be the brightest in that section of the sky. It isn’t.

Capella is one of our brightest stars, and you may catch it this month just peeping up over the northeastern horizon about an hour and a half after sunset. And it is brilliant!  When you see Capella,  compare it with the North Star  and you will get a good idea of what the word magnitude means. There are a solid two magnitudes difference between the two – or if you want to get technical, Capella is magnitude 0 and Polaris is magnitude 2.

Yes, the magnitude system goes backwards – the lower the number, the brighter the star. Each magnitude difference represents a change of about 2.5 times in brightness. So a zero magnitude star is 2.5 times as bright as a first magnitude star – and 2.5 x 2.5, or 6.25 times as bright as Polaris, a second magnitude star. And while we’re on this subject, the faintest star in the Little Dipper – it’s over in one corner of the cup – is just about magnitude five. That means Capella is 100 times as bright as that star. (OK – if you actually do the math it doesn’t come out because I rounded off the difference – it’s really 2.512 for those wanting more precision.)

In fact, there is another interesting way to look at that star – at magnitude 4.9 it is almost exactly what our Sun would look like if it were placed just 32.5 light years away. At that distance our sun would be magnitude 4.8 – and that distance is the distance we use to compare stars. That is, to get an “absolute magnitude” for them so we can compare apples with apples,  we ask ourselves how bright a star would be if it were 32.5 light years from us.

And while we’re on the subject of magnitude, the Little Dipper does give us a great range. Polaris, as we said, is magnitude 2. The other bright star in the Little Dipper is magnitude 2 also – it’s at the end of the cup away from Polaris. Sharing that end is a magnitude 3 star, and these two are known as the “Guardians of the Pole” as they are prominent, close, and like other stars, circle around the pole  every 24 hours. Most of the other stars in the Little Dipper are magnitude 4, with the one star in the corner of the cup being magnitude 5, as noted – well, actually 4.9. There’s a chart with these magnitudes in this post. Many people who live in light-polluted areas can see only three stars in the Little Dipper – Polaris and the two Guardians of the Pole.

How faint a star can you see? Depends upon your eye sight, the light pollution in your area, the transparency of the skies on any given night, how high the star is in the sky, and, of course, your vision and dark adaption. But as a general rule of thumb magnitude 6 has been accepted as the typical naked eye limit. However, if you live in a typically light polluted suburb you may see only to 4, or worse yet, magnitude 3. And observers on mountain tops with really clear skies reliably report seeing stars as faint as magnitude 8. All of this is with the naked eye. Add ordinary binoculars and you will certainly add three to five magnitudes to the faintest star you can see. In fact, you take a huge jump in the number of stars seen just by using binoculars with 50mm objective lenses. That’s why many amateur astronomers with fine telescopes also are likely to have a pair of 10X50 binoculars that they keep handy. I always did, but more recently I stumbled upon some very inexpensive Celestron 15X70 binoculars that I love for quick peaks, though they are two powerful and large to hold steady for serious observing.

Capella will be a “look east” guide star next month, but you can get to know it this month as you look north. And if you live in mid-northern latitudes, it will become a most familiar site. In fact, where I live – about latitude 42°N – it is in the night sky at some time every night of the year. This is because it is so far north that as it circles Polaris, it only dips below the horizon for a few hours at a time.

Look East In January 2013 – King Jupiter, plus a trio of twins; Orion, man of the world; Betelgeuse, giant among giants!

January 2013 brings the usual host of bright and wondrous winter stars – and one star that isn’t, but outshines them all – Jupiter. The “king of the planets” is absolutely dominant in the eastern sky this month, even though it gets a tad dimmer as the month goes on.  As we put some more distance between us and it, it drops from -2.7  at the start to -2.5 at the end of the month –  good luck on even being able to notice the change!  At magnitude 0 Capella is the brightest star we see, though in an hour or two, Sirius at Magnitude -1.5 will be up and come significantly closer to Jupiter’s brightness – but Jupiter will still dominate.

There are four new guidepost stars to meet this month and one new guidepost asterism, Orion. Orion is probably the best known figure in the heavens because it actually looks like a person and can be seen from most locations in the world since it’s centered on the celestial equator. That’s a lot for one month, but fun to think about on a dreary winter day and more fun to observe on a brilliant, winter evening. Here’s the chart for the eastern sky one hour after sunset for mid-northern latitudes. Remember, going out about 45 minutes to an hour  after sunset and looking east, you’ll see only the brightest stars as they come out. This makes it easier to identify and learn our guidepost stars. Our guidepost asterisms may not be as readily seen until a little later as the sky gets darker and more of the fainter stars come out.

lookeast
The eastern sky as seen on a January evening about one hour after sunset. Click image for larger version. Use link below to download a printer-friendly, black and white version of this chart. (Chart is based on a screen shot, modified by me, of Starry Nights Pro software.)

Click here to download a black-on-white (printer-friendly) version of this chart

The January eastern sky – what to remember

 Castor – A trio of twins When you see Castor, think “twins” – a trio of twins. Well, in a sense there are really four pairs!

Castor is one of the Gemini Twins (Castor and Pollux), but in a small telescope we see it really is three stars, Castor A, Castor B, and Castor C - and though we can't see this in our telescopes, each of these stars is really a pair, making six stars in all!
Click image for larger view.

But the fourth pair is just mythological – Castor is one of the “heavenly twins” of the constellation Gemini – the other twin being Pollux. This is nothing but a fanciful relationship, though, based on how the stars appear to us – and appeared to ancient cultures as well. But there is more, much more, to Castor. And, it’s what we don’t see that makes this bright star so fascinating. And seeing withy our mind’s eye – your knowledge of what you are seeing – always enhances your experience under the night sky. So were you to look at Castor in a backyard telescope, you would see it has a twin – another bright star that appears quite close –  the two are known simply as Castor A and B. These two are related, orbiting one another about every 400 years. But there’s more. Each of these two are twins! However, you can’t see this in a telescope because in both cases the pairs of stars are extremely close to one another, orbiting one another in periods of less than 10 days. And as noted, each pair orbits the other pair in about 400 years. But there’s more. Returning to that backyard telescope you may notice a third star, Castor C, quite a distance from the first two and significantly dimmer. This star is also part of the Castor family and it too has a twin that also is so close we can’t detect it without special instruments. In fact, Castor C consists of the closest pair of all, orbiting one another in less than a day! This pair, in turn, orbits the other four stars in the system once every 10,000 years or so. So when you look at Castor, remember that in classic mythology it has a twin, Pollux – and remember that what looks to you like a single bright star is really the combined light from six stars, all held together in one of the most complex star systems we know. (I wrote much more about the Castor system on the double-star blog. That post includes a scale model that puts Castor and company into perspective with the Earth and Sun. You’ll find it here. )

Vital stats (for just the brightest star in the Castor system):

  • Brilliance: Magnitude 1.58, the 23rd brightest star in our sky and the brightest second magnitude star. Absolute magnitude is 0.9. (Yes, we call a star “second magnitude” if it’s magnitude is between 1.5 and 2.5 – so you can see castor just slips into this category.)
  • Distance: 50 light years (not among the 200 nearest stars)
  • Spectral Type: A
  • Position: 07h:34m:36s, +31°:53′:18″
  • Compared to the Sun: Castor radiates 14 times as much energy as our Sun.

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Getting to know Pollux – the bigger, brighter twin

How Bayer saw the Gemini Twins in his 1603 atlas. (Image courtesy of Linda Hall library of Science, Engineering and Technology.)

Pollux should feel a little cheated because it’s the brightest star in the constellation of Gemini and usually the brightest star was given the designation “alpha”  by the early chart maker, Bayer. Not Pollux. It is designated “Beta Geminorum” and follows its slightly dimmer twin brother around the sky. But Pollux has its own way of standing out: It has a slight edge in brilliance in our skyit is a tad closer to us; and it is an orange giant. What’s more, in 2008 it was confirmed to have a planet orbiting it. As an orange giant, it has moved off the “main sequence,” and instead of fusing hydrogen into helium, as our Sun does, it is fusing helium into carbon and oxygen. It will eventually blow off a lot of its substance becoming a planetary nebula. It is currently about eight times the diameter of our Sun – that’s huge, but nowhere near as large as our next star, Betelgeuse. The planet circling Pollux is also large – “Jupiter class” – and was first detected in 1993, but not confirmed until 2008.

Vital stats:

  • Brilliance: Magnitude 1.14, the 17th brightest star in our sky. Absolute magnitude is 0.7 .
  • Distance: 34 light years (not among the 200 nearest stars)
  • Spectral Type: K
  • Position: 07h:45m:19s, +28°:01′:35″

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 Orion – A man for all to see

If you’re in the same general latitude as I am in Westport, MA, then you see Orion like this as it rises in the east on a January evening.

Orion – as seen when rising in mid-northern latitudes. (Click for larger image.)

What always sticks with me about Orion is how Robert Frost described him in his wonderful poem, “The Star Splitter.”

‘You know Orion always comes up sideways. Throwing a leg up over our fence of mountains, And rising on his hands, he looks in on me . . .

But if I lived in Sydney, Australia, I wouldn’t see it this way. What I would see is a man standing on his head!

Orion, as seen when rising in the east from Sydney, Australia. (Click image for larger version.)

The real point here is that these stars do look like a man, and they can be seen from deep into both the southern and northern hemispheres. What’s more, the three distinctive stars that form Orion’s belt also mark the approximate position of the celestial equator in your sky, a handy thing to know. Of course, if you’re in the southern hemisphere, the celestial equator appears to make an arc across your sky to your north. In the northern hemisphere it appears to make an east-west arc across the sky to the south. But in either case the belt stars of Orion will rise just about due east and set due west. How high they get in your sky is calculated simply by subtracting your latitude from 90. That is, if your latitude is 42 degrees, as mine is, then Orion’s belt will be, at its highest, about 48 degrees above the horizon when it passes due south. From Sydney, Australia, the stars in the belt will cross about 56 degrees above the horizon as they pass due north. And yes, if you live on the equator these stars will cross directly over head. Anyway you look at it, Orion is a man for all latitudes – well, almost. At the north pole you would only see his top half, and at the south pole, only his feet! Return to Menu

Betelgeuse – giant among giants – and Rigel’s pretty large as well!

When you look at the eastern sky early on a January evening, get this picture in your head!

Here’s what our eastern sky would look like on a January evening if Arcturus and Rigel, two genuine giants, were as near to us as our Sun. The Sun, to scale, is also shown. Betelgeuse is NOT show to scale.

Yes, that’s rigel represented inthe illustration, not Betelgeuse. Classified as a red supergiant, Betelgeuse is one of the largest stars you can see – and certainly up there with the biggest of all stars – yet it doesn’t look any bigger in our sky than other stars because all stars, except the Sun, are so far away they appear only as a point source of light to our eyes. Last month we showed what Aldebaran would look like if it were in our sky and the same distance from us as the Sun, and this month we’ve added Rigel to the picture. But we can’t do a similar thing with Betelgeuse – it wouldn’t be in our sky – it’s so large we would be in it if it were located where our Sun is! What’s more, it’s hard to put a number to the size of Betelgeuse, not because it can’t be measured, but because it’s hard to decide exactly what you want to measure when you’re dealing with a ball of gas – especially one like Betelgeuse. Our Sun is a little easier case. While it does not have a surface, it does appear to us to have an edge that’s fairly easy to define – it’s the place where its gases are dense enough to be opaque to our vision. Exactly how we define the size of Betelgeuse is a bit more difficult. I rely on James B. Kaler as my stellar authority. I love his books, and in one, “The Hundred Greatest Stars,” he describes the size of Betelgeuse variably as:

  • 650 times that of the Sun, or 2.8 AU (Astronomical Units – an Astronomical Unit is the distance between the Earth and the Sun – roughly 93 million miles)
  • 800 times the diameter of the Sun, or about 4 AU
  • 1600 times the Sun – about 8 AU when measured by modern observation in ultraviolet light

And on his Web site, after opting for a figure of around 8-9 AU, he writes:

However, the star is surrounded by a huge complex pattern of nested dust and gas shells, the result of aeons of mass loss, that extends nearly 20,000 AU away (Betelgeuse so far having lost over a solar mass). That, an extended atmosphere, and the pulsations make it difficult to locate an actual “surface” to tell just how large the star actually is. Moreover, because of changes in gaseous transparency, the “size” of the star depends on the color of observation.

Betelgeuse has other problems. The pulsations he refers to are a sort of puffing up that occurs from time to time and changes both size and brightness significantly. Betelgeuse is usually thought of as about magnitude 0.55, but it can be as bright as 0.3, or as dim as 1.1. All this huffing and puffing will soon lead to an explosion, and Kaler says it will then be as bright as a crescent moon! But don’t hold your breath. “Soon” in astronomical terms means sometime in the next million years or so! Its distance, too, is uncertain, but 500 light years is a good ballpark figure. Let’s focus on that 8 AU size for a moment. When we build a scale model of our solar system and reduce the Sun to something about the size of a volleyball, the tiny speck of the Earth orbits at around 75 feet away. But at 8 AU Betelgeuse would be more like 600 feet in diameter. So pause for a moment as you look at Betelgeuse on a winter evening. Imagine yourself holding an 8-inch volleyball in one hand – our Sun – while you stand next to a red, raging, unstable monster ball that is 600 feet in diameter!

Vital stats:

  • Brilliance: Magnitude 0.3 – 1.1, the 10th brightest star in our sky (sometimes). Shines with the luminosity of about 90,000 Suns.
  • Distance: 570 light years
  • Spectral Type: M
  • Position: 05h:55m:10s, +7°:24′:25″

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Rigel – Blue and brilliant

Here we go again! Like Pollux, it looks like Rigel was short-changed having been designated the “Beta” star of the constellation Orion while dimmer Betelgeuse is the Alpha. Of course, Betelgeuse, being variable, may have been brighter when Johann Bayer made his designations in 1603. Bayer’s “system” is inconsistent, however, to say the least, so there’s no sense getting too worried about this. Like Betelgeuse, Rigel is a supergiant. It’s huge and it’s brilliant too – and since it is more distant (860 light years), it is intrinsically more brilliant than Betelgeuse. Jim Kaler writes: “Only about 10 million years old, Rigel should eventually expand to become a red supergiant very much like Betelgeuse is today, by which time it will be fusing helium into carbon and beyond in preparation for its eventual explosion as a supernova.” Rigel’s radius is 74 times that of the Sun, 0.34 Astronomical Units, nearly as big as the orbit of Mercury. Rigel is a challenging double star for amateurs with moderate-sized telescopes.

Vital stats:

  • Brilliance: Magnitude 0.12, the 7th brightest star in our sky. Shines with the luminosity of about 90,000 Suns.
  • Distance: 860 light years
  • Spectral Type: B
  • Position: 05h:55m:10s, +7°:24′:25″

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Look East in December 2012 – see Jupiter and take the Pleiades challenge!

“Glitter like a swarm of firefliesTangled in a silver braid.”  – No you don’t see the Plides star cluster quite like this with your naked eye, but binoculars and small telescopes give you an awesome view. (Words from Tennyson, photo from NASA.)

The focus for those learning the stars this month is the beautiful star cluster, the Pleiades, and while charming to those with dark skies and good eyesight,  I guarantee you it will look far better in just about any binoculars you point towards it.   But in December 2012 you also have Jupiter dominating the eastern sky in early evenings – it’s by far the brightest “star” there. This is also a great  year for the annual Geminid shower, Mercury puts in its best appearance of the year in the morning sky, and Ceres and Vesta offer a special challenge fror those who would like to use their binoculars to spot a dwarf planet and an asteroid. You can find all the details for these in this month’s  “events” post found here.

Here we’ll focus on the sky spectacular that happens every December when you look east starting about 45 minutes to an hour after sunset. Here’s what you should see.

Click image for larger version. (Prepared from Starry Nights screen shot.)

Click image for larger version. (Prepared from Starry Nights screen shot.)

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

Capella, which we met last month, dominates the northeast and now it’s easy to pick out the familiar kite figure which, lead by Capella, covers the heart of the constellation Auriga. About parallel with Capella, but south of it will be the Pleiades – but don’t expect to see them well until it gets darker. You may pick them up with binoculars an hour after sunset, but to really appreciate them, wait until an hour and a half after sunset.

East of the Pleiades – below it as you look at the eastern sky – is the bright guidepost star, Aldebaran. This month Jupiter is so close it tends to drown out the glory of Aldebaran.  Aldebran  highlights a “V” asterism that marks the head of Taurus the Bull.  You can fit Aldebaran, Jupiter and much of this “V” – which is the Hyades star cluster, into the same low-power binocular field of view. Imagine just for a moment what it would be like if Aldebaran were our Sun. James Kaler points out that it would span 20 degrees in our sky – our Sun spans half a degree! So rising in the east, it would nearly fill the space between the Pleiades and the horizon. Get the following vision of Aldebaran in your head as you gaze to the east on a December evening.

Aldebaran, looking like the “Great Pumpkin” of Peanuts comic fame, would overwhelm us with its orange brilliance and dominate our sky if it were as close to us as our Sun. (Actually, if we were this close to Aldebaran we would be overwhelmed – charred to a crisp!)

Aldebaran is what is classified as a “giant,”  and it is indeed huge when compared to our Sun, but there are many stars much larger. It’s the 14th brightest star in our sky – compare it to Capella and you will notice that Capella is  brighter.  (Again, in 2012 Jupiter will tend to dominate Aldebaran making it seem a bit less than it is when it has this corner of the sky to itself.) Aldebaran is 67 light years away – reasonably close – and in the ecliptic – the path the Sun, Moon, and planets take in our sky. This means it frequently flirts with Mars and at such times it’s fun to compare the color of these two reddish objects. It also gets occulted, from time to time, by our Moon – meaning the Moon passes in front of it. Its surface temperature is a bit lower than our Sun’s, thus the orange tint. It radiates quite a lot of its energy in infrared and is about 425 times as luminous as our Sun.

Vital stats for Aldebaran (al-DEB-ah-ran)

• Brilliance: Magnitude .85; its luminosity is the equal of 425 Suns.
• Distance: 67 light years
• Spectral Types: K5 Giant
• Position: 04:36, +16:32

Aldebaran appears to be the brightest star in another star cluster, the Hyades. (The “V” to the south of it.) In reality, it is not part of that cluster, for it’s much closer to us. The Hyades are about 153 light years from us.)  Its name – Aldebaran – means “follower” – for it appears to follow the Pleiades up the sky.  (Actually, skywatchers sometimes use the terms “precedes” and “follows” to indicate sky direction. A star that “follows” is to the east of the object it is following – and one that precedes, is to the west.)

In classical depictions of the constellations, Aldebaran is the “bull’s eye,” and  the “V” of stars near it is the bull’s head. But that V is, as mentioned ,  another open star cluster, the Hyades.

Taurus, as depicted in Uranometria (Bayer, 1603), showing Aldebran as one of his eyes. (Used with permission from the  Linda Hall Library of Science, Engineering, & Technolog.)

Hyades and Pleiades

Now what’s fun here is to pause a moment and go back and forth between the Hyades and the Pleiades. Both are open star clusters, and in reality they cover roughly the same area of space – about a dozen light years – but, you will notice immediately that the Hyades appear much larger. There’s a simple reason for that – the Hyades are just 151 light years away, while the Pleiades are more like 400 light years from us.

A careful observer will also notice that the Hyades tend to be yellowish stars, while the Pleiades are icy, blue diamonds. That’s because the Hyades at 660 million years are about ten times as old as the Pleiades. Of course, in astronomical terms both contain young stars, our Sun being about 5 billion years old and our galaxy something like 12 billion years. But the few hundred million years of age the Hyades has over the Pleiades means it does contain more yellow stars.

One more thing you might notice about the Pleiades – they look like a tiny dipper – in fact, I’ve had more than one visitor ask me if this is the “Little Dipper.” I guess you could call it The Littlest Dipper! You also could call it “Subaru”  as the Japanese do.  That’s their name  for  this little purse of celestial gemstones,  and the car maker does include them in its logo. And here are a couple of Pleiades challenges for you:

1. How many Pleiads can you see with the naked eye?

2. And can you see – with naked eye, binoculars, or telescope – the faint nebulosity that surrounds these stars?

It was that nebulosity that apparently inspired Alfred Lord Tennyson as he penned this famous tribute in “Lockesley Hall”:

Many a night I saw the Pleiades,
Rising thro’ the mellow shade,
Glitter like a swarm of fireflies
Tangled in a silver braid.

Beautiful, but no words or image can do justice to the live, real-time experience of standing outside on a crisp December evening, raising binoculars to your eyes, and seeing these icy diamonds! (Oh they can be seen with the naked eye, but binoculars give a much better view.)

Even without binoculars, the Pleiades can be quite dazzling for those with good eyes and dark skies. Not me. With my aging eyes they tend to blend together, and even when I put my glasses on I can only with care see four or five separate stars. Younger eyes do much better.

So how many stars do you see? Take your time. Patience is the key. I suggest you get a comfortable beach chair, lean back, relax, and look for at least a solid minute at a time.  How many should you see? I suspect most people who take the time to observe carefully get as many as six to 10.  Walter Scott Houston, who wrote a Sky and Telescope magazine column when astronomy was new to me in the 1950s, counted 18 with the naked eye! And the visual observer I most  admire today, Stephen James O’Meara, says in his book “The Messier Objects:”

Although largely symbolic, the age-old association of the Pleiades with the number seven remains fixed to this day – to the point that some observers swear they cannot see more than seven members, even though the Pleiades contains 10 stars brighter than 6th magnitude. Some observers question how it is possible to see 10 Pleiads in The Seven Sisters (a demonstration of the power of words . . . ) The fact is that almost three times that magic number of stars can be seen without magnification by an astute observer under dark skies.

O’Meara says he logged 17 while observing in Cambridge, MA – which hardly has dark skies.  “The trick,” he says, “is to spend a lot of time looking and plotting.” This business of “time on target” is something I find hard to convey to new observers. But it is the key. Another key is simply experience. I frequently see things that those with younger eyes don’t see, simply because I’ve seen them before and know exactly what to expect. Crossen and Tirion in their book “Binocular Astronomy” have this general piece of advice, which certainly applies here:

When I first began observing with binoculars I could not see the Rosette Nebula at all, but now it is not difficult for me even under poor sky conditions.
The most important thing in observing is to really look – a mere glance at an object or a field is simply not enough. You must keep your eye at the oculars for at least a full minute at a time.

That said, don’t let the numbers and reports by others discourage you – the Pleiades are yours to enjoy no matter how many you count.  Another noted popular astronomy author, Terrence Dickinson, writes in his book “Nightwatch,” that he has “a tough time seeing more than six stars with the unaided eye, even under excellent conditions,” but he also notes that some of his “astronomy students have reported seeing as many as 11.”

And turn binoculars on them and you should be able to easily count between 25 and 50.

The second challenge is more subtle. It involves the nebulosity that shows up in nearly every photograph of this cluster. No, don’t go looking for such a photograph. It will only prejudice you as to both the nebulosity and the fainter stars – and besides, you’ll never match a long exposure photograph with your eyes because film, or the modern CCD accumulate  much more light than our eyes.

The Pleiades, as I mentioned, are “young” stars – roughly 100 million years old, and in astronomical terms that means they’re mere babes. (Our star – the Sun – is about 5 billion years old. ) The Pleiades are not far removed from the cosmic womb of gas and dust in which they were formed. Until fairly recently it was assumed that this nebulosity we see was the last wispy remains of the nebulae in which the Pleiades were formed. Today it is more generally thought that this nebulosity is just a happy accident – an entirely different gossamer cloud of gas and dust that is reflecting the brilliant light of the Pleiades as they pass through it.

In any event, Tennyson seems to reference it when he refers to his “swarm of fireflies” being in a “tangled braid.“  When I look with the naked eye I certainly don’t see it. But be careful. A couple of these stars are quite bright, and because they’re close together, their light tends to blend and perhaps give the impression of being surrounded by nebulosity. Perhaps that’s all Tennyson saw, especially as the stars were near the horizon – or at least that’s where he puts them in his poem.

So while I assume Tennyson was talking about a naked eye view and perhaps glimpsed the nebulosity in pristine Victorian skies free of modern light pollution, I feel this second challenge is best pursued with binoculars and small telescopes.  While there is nebulosity near several stars, the brightest part is southeast of Merope. (Merope is identified in the downloadable charts at the end of this section.)  So I would look for this first.  What you need to do is look for a difference in the darkness of the background sky in this region. Using binoculars move away from the cluster a tad to avoid the glare – see how dark the sky is? Now move closer to it – do you detect any change in the background brightness?  Again, be careful you don’t confuse the glow around a bright star with nebulosity.

When you think you have spotted the nebulosity, it would be helpful to quickly sketch its location on the provided chart – then compare it with a picture of the Pleiades, such as this one, to see  if your impression of the location and size of the nebulosity matches what the camera reveals.

When to look

To take the challenge you want the Pleiades high in a dark – moonless – sky. In December of 2012  the Pleiades can be seen in moonless skies in the early evening for the first couple weeks.  The last couple weeks of the month you’ll probably find yourself hindered by varying amount of moon light.

This is a good lesson, however, for looking at any faint astronomical object. When we do that we are constantly balancing these different factors of how high the object is above the horizon – the higher the better because the higher it is the less atmosphere you need to look through to see it – and where the Moon is, because it is constantly changing position and brightness, and it tends to wash out the sky anywhere near it.  But as you can see, there’s at least a two-week window when you can take the Pleiades’ challenge – assuming the weather cooperates! And, of course, the Pleiades will still be with us through the winter.

Some helpful charts

Click image for larger version. (This chart is derived from a Starry Nights Pro screen shot. A printer friendly version appears in the links at the end of this post.)

There are three printer-friendly charts listed here, but for starters I suggest you download only the first two. They both show the brightest Pleiads but the second one has no names on it and is meant for you to use – and add to – when taking either challenge. Put it on a clipboard and take it, a pencil, and a soft red light to your observing location. Then when you spot a faint star you can mark its location in relation to the brightest stars. Once you’ve done this, take a look at the third chart which shows the Pleiades as seen through a typical pair of binoculars. This chart will tell you whether fainter stars you identified and noted on your chart are in the sky or just in your imagination 😉

Chart 1 – Download this chart as a starting point for your observations – and to get to know the names of the Pleiads. (Atlas and Pleione are the parents of the seven sisters.)

Chart 2 – Download this chart to use for note-taking while you’re observing.

Chart 3 – Download this chart to check for faint stars you detected to see if you marked them in the right position.

Finally, compare your observation of the nebulosity with a picture of the Pleiades, such as this one.

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