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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 January 2013 – an “engagement ring” points the way to the true celestial pole

About one hour after sunset, look north and you should see a sky similar to the one shown in our chart – assuming you live at mid-northern latitudes. The height of Polaris, the North Star, will be the same as your latitude. Polaris stays put. Everything else appears to rotate about it, so our view of all else changes in the course of the evening – and from night to night. It’s a good idea to check the north sky every time you observe to get a sense of how things are changing and to orient yourself.

Click image for larger view. Chart derived from Starry Nights Pro screen shot.

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

Of course, Polaris – the “North Star” – is really not exactly north. It’s just a very good approximation of north. True north in the sky is the North Celestial Pole – a projection of the Earth’s north pole – and it would be too much to hope that a bright star would be parked on this exact spot. But if you have binoculars, point them at Polaris on a dark, clear night – one where there’s no interference from the Moon – and you should be able to see a neat little asterism called the “Engagement Ring,” a crude ring of 7th and 8th magnitude stars with Polaris forming the diamond. Look carefully and you’ll see this ring tells you the direction and distance to the true north celestial pole.

The North Celestial Pole is to the north of Polaris (arrow), and the Engagement Ring asterism extends to the south of it. You can use the diameter of the Engagement ring as a rough guide as to how far away – in the opposite direction – the North Celestial Pole is from Polaris. Field of view here is about 4.5 degrees as seen with 15X70 binoculars. Lower power binoculars will show a larger field. Click for larger image. (Prepared from Starry Nights Pro screen shot.)

Of course, Polaris, as with the other stars, travels in a great circle around the pole. But, the relationship between the Engagement Ring, Polaris, and the true North Celestial Pole, remains the same, and south is defined as the direction away from the pole, north the direction towards the pole, and west is the direction the stars appear to rotate. For more on finding directions in the night sky, see this post. See the movie below, made with Starry Nights Pro software, to see how Polaris and the Engagement Ring rotate around the celestial north pole in the course of 24 hours.

High above Polaris the familiar “W” of Cassiopeia has completed its transition to an “M” as its stars roll around the pole. Off to the northwest near the horizon we see two bright guidepost stars, Vega and Deneb. To the northeast we have brilliant Capella.

The Big Dipper is easy to spot because it’s stars are bright. But folks frequently have trouble with the Little Dipper  and that’s no surprise because many of its stars are faint.  So don’t be alarmed if you can’t pick out most of the Little Dipper stars – four of them are fourth magnitude or fainter and besides, they are below Polaris this month, making them even more difficult to see since you are looking through more atmosphere when stars are low. I see them only when it has become fully dark – about 90 minutes after sunset – and when my eyes have had 10-20 minutes to dark adapt.

Look North in December 2012 – seeing red yet?

That’s “red” as in garnet, for William Herschel’s Garnet Star, which is particularly well placed for observation in our northern sky in December, though it may take binoculars to bring out the color. OK, I’m getting ahead of the game. First let’s take a look at what the north sky looks like about an hour after sunset on a December evening from mid-northern latitudes.

Click image for larger chart. (Modified screenshot from Stellarium.)

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

Highest of the circumpolar constellations this month is Cepheus, which I always see as a home plate – and in December, a home plate pointing roughly downward towards Polaris, the North Star. We discussed Cepheus in some detail in September. And if you’ve been following these “Look North” posts for several months you’ve also met the “W” of Cassiopeia, the “Bow” of Perseus (both to the east) and the slithering form of Draco the Dragon to the west, curling its way up, then down, and finally between the Little Dipper and the Bigger Dipper, which now is hugging the northern horizon. But what about that garnet star? Where’s that? High on our chart. Let’s zoom in on the “home plate” of Cepheus.

Click image for larger chart. (Labels added to Stellarium screenshot.)

Go here for a printer friendly version of this chart. 

Now the big question is – will this star really look red? I would say emphatically “yes!” – if seen in a telescope. “Probably,” if seen with binoculars, and “perhaps,” if seen with the naked eye. Star colors are better described as “tints.” They are very much real and relate directly to the surface temperature of a star – but they are frequently difficult for beginners to see, and I’ve met some experienced observers who swear they can’t detect color in stars.

One reason is our eyes are simply not designed for it. We see color only when the light is bright. In dim light we see in black and white. Because telescopes gather more light, it is more likely that a star seen in a telescope will show its true color. But binoculars gather a lot more light than our naked eye, so they also help significantly when trying to detect color. And in this case we’re talking about a very red star known for a couple centuries as “William Herschel’s Garnet Star.” He described it as “a very fine deep garnet color . . . .”

Looking recently with binoculars  I really could not detect much color with 8X40 glasses. With 10X42 I could see some. With 11X56 it clearly had a reddish tint – and with 15X70 glasses I had no doubt that I was looking at the “Garnet Star.”

OK, my font color choices in this software don’t give me garnet, so I’ve been using red in this post. But this shot of the mineral garnet really looks – at least on my computer display – hauntingly like the tint I see for Mu Cephei in my telescope. What do you see? Mu Cephei is a variable, so if you happen to catch it near its brightest, it should be easy to pick out with the naked eye. Catch it when dim and it will be down in the range of the fainter stars of the Little Dipper. I haven’t studied it in binoculars – that’s on my observing list for this December – but Gary Seronik in his “Binocular Highlights” book says that “even in 10X30 binoculars Mu appears distinctly yellowish orange and is easy to identify in a pretty field because of that.” And once you identify it, ponder these facts, gathered from James Kaler’s “The Hundred Greatest Stars.” Mu Cephei is:

  • among the most luminous and largest stars in our galaxy
  • about 2,000 light years away
  • shining through lots of interstellar dust that diminishes it by about 2.5 magnitudes
  • radiates 350,000 times more energy than the Sun
  • has a radius that would mean that if placed in our Solar System it would engulf Mercury, Venus, the Earth, Mars, the asteroid belt, Jupiter, and reach nearly halfway to Saturn
  • is in a variable stage, is unstable, losing mass, and will “surely explode someday”

Of course “someday” to astronomers could mean millions of years. Don’t go out there assuming you might catch it going out in a blaze of garnet glory! Just go out there and enjoy this wonder of the universe. Oh – and that “variable stage” means it does change in brightness in an irregular fashion going up or down about a magnitude and a half. That’s one more factor that could impact how red it looks to you – catch it near it’s peak – magnitude 3.6 – and it should look redder simply because the more light we see the easier it is to see red. near minimum it is about magnitude 5 and the changes takes place irregularly over a period of 2 – 2.5 years.

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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