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    My Journey through the Astronomical Year

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

Prime Time Observing for December 2009 – take the Subaru Challenges!

“Subaru?”  Yep! That’s the Japanese name  for a little purse of celestial gemstones better known in the West as the “Pleiades,” or in many cultures throughout the world as the “Seven Sisters” or some variation of that idea.  And  yes, I said “challenges” – plural, because there are two:

1. how many Pleiads can you see with the naked eye?
2. and can you see – with naked eye, binocular, 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! And yet all that “cold” blue light really indicates they are very young, very hot stars, all of which are part of an open cluster. But more on that in a minute.  For while the Pleiades lead the observing agenda for any December, in 2009 we have some other great choices as well, including a splendid meteor shower and four nice planets to view – five if you want to get up early. And we’ll add the Pleaides “follower”  – the huge reddish star, Aldebaran – to our list of guidepost stars as well.

So let’s take a look at this month’s prime time chart – a chart that applies to the eastern sky as seen from mid-northern latitudes, 45 minutes after sunset as usual, but with this quibble – you  may not see the Pleiades that early. If you don’t, try locating November’s guidepost star, Capella, in binoculars and sweeping south (to your right), or locate Aldebaran, and sweep upwards with your binoculars. The Pleiades should pop into view. If you still don’t find them, just wait, they’ll appear as the sky gets darker. In any event, you’ll want to wait until later if you’re going to take the challenge. So here’s the chart with our new star, Aldebaran, front and center. Yes, Aldebaran – an Arabic name which means “the follower” and refers to the way this star seems to follow the Pleiades across the sky – and who wouldn’t!

Also, we’ve added a “kite” asterism with Capella – last month’s guidepost star now highinthe northeast – as the dominant star int he asterism. (This is actually the classic constellation Auriga, the Charioteer, but I think the Kite is easier to see and remember.)

Click image for larger view. (Chart derived by modifying Stary Nights Pro screen shot.)

Click here to download  a black-on-white version of the preceding chart, suitable for printing in landscape format.)

OK – here are the highlights we’ll be covering this month:

  • The Pleiades makes a challenging sight for naked eye observation – how many can you count? And they’re a delightful sight in binoculars or small telescopes  – but can you see the nebulosity?
  • The Geminids meteors should put on a terrific show with no interference from the new moon on December 13-14.
  • We draw closer and closer to Mars as we chase it down in our orbit around the Sun and this makes it both brighter to our naked eye and bigger in our telescopes.
  • And speaking of telescopes, great Jupiter, dropping low in the southwest, has its third and last – for several years – close encounter with Neptune.
  • And yes, Saturn is back for early risers with rings that are becoming much easier to see again in asmall telescope!

The Pleiades (Subaru) challenges

Even without binoculars, the Pleaides – also known as “M45” and “the Sevens Sisters” –  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. A recent 6-year-old visitor to Driftway Observatory saw them – as many adults do – as the “Little Dipper.” Well the six brightest stars do form a tiny dipper, but the real Little Dipper isn’t nearly as dazzling, is much larger, and is in the north, not the east.

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 – less than 50 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.

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 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 2009 your first opportunity for this will  be around December 5 or 6th.  The Pleiades will be well up about two and a half hours after sunset, and the Moon will not have risen at that time.  As the month progresses, you can wait later and later without interference from the Moon because the Moon rises later each night until New Moon. (And later is better because the Pleiades will be higher in the sky.) Until  about December 19 or 20th – by then the Moon is in the western sky when you look – far away from the Pleiades, but still likely to make it difficult to see the faint stars and nebulosity.  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 its constantly changing position and brightness wash out the sky anywhere near it.  But as you can see, there’s a solid two-week window when you can take the Pleiades challenge in the middle of this month – 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 froma Starry Nights Pro screen shot. A printer firendly version appears in the links which follow.)

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 something 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 Pleaides 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 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,

The Geminids show December 13-14

Click image to get an enlarged version. (Modified from Starry Nights Pro screen shot.)

(Download a printer friendly version of the preceding chart. )

This is a terrific meteor shower because unlike the Perseids in August and the Leonids in November, you don’t have get up at 3 am for a good view – though for East Coast observers  midnight is best this year, though plenty of meteors should be seen earlier. The radiant point for this shower is in the constellation Gemini and it is already above the eastern horizon as it gets dark.  By about four hours after sunset it is well up in the east. Since the meteors appear to radiate from this point – and you can see them anywhere in the sky – then at this stage more than half the shower meteors should be above the local horizon. So it is really worth it to start looking as early as 7 pm on December 13.

However – there’s always a however – the shower this year is due to peak at 5 hours Universal Time. That translates to midnight EST December 13/14. So my personal plan is to start looking for these meteors at 11 pm and keep looking until 1 am EST.  That gives me the best opportunity to see the most meteors, assuming the weather cooperates.

Here are some tips to get the most out of this shower no matter where you are and when you look:

1. Look up – constantly! Geminid  meteors can appear in any section of the sky – it’s just if you traced them backwards they would seem to come from one area near the constellation Gemini.  (Yes, you’ll see more most likely if you look in the general direction of the radiant point, but you may miss some too, so don’t hesitate to look around at other sections of sky.  When I say “look up” I’m not being facetious. Meteors wait for no man or woman – and there’s no instant replay. I’m amazed at how many meteor watchers don’t follow this simple rule – they talk to companions, and seem to look around at or near ground level, and then grumble when someone else spots a brilliant meteor that they missed.

2. An adjustable beach chair or lounge is great, as well as a sleeping bag or blankets. Even in warm climates, you get cold sitting still for an hour or more under a clear sky.  You’re just one big radiator sending off heat to the universe!

3. Bring binoculars and when you see a bright meteor, use them! Look where the meteor just appeared and you are likely to be rewarded by seeing the trail of smoke it leaves. You may be able to watch this for several seconds as the winds in the upper atmosphere start to twist and disperse it.

Finally, just enjoy being out there. The stars of winter are especially brilliant, not because the skies are clearer and drier (in the northern hemisphere they may be) but because there are simply more bright stars, especially in the region around the constellation Orion, which can be see from just about anywhere on Earth.

Chasing Mars

Here’s the thing – Mars and Earth are closest to one another every 2.1 years – but exactly how close they get each time varies over  a 16-year cycle.So we get close every 2.1 years, but the closest approach happens about every 16 years. This means that some close approaches are much better than others, so the best views of Mars happen every 16 years! And where are we now in that 16 year cycle? Somewhere near the bottom. But play the hand you’re dealt. If you want the best view of Mars in a backyard telescope, then the next four months offer you the best chance you’ll have until about 2014. (In 2012 it will actually be a little worse than this time.) On a positive note, this time Mars is relatively high in the sky for Northern Hemisphere observers and its fun for naked eye observers to just trace its path among background stars. This chart provides you with a starting point for Mars in mid-December.

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

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

Mars will change constantly in December. Each night it will rise earlier and be a bit brighter, doubling in brightness from the beginning to the end of the month – but still outshone by Sirius.  Its position against the background stars also changes. For most of the month it appears to move in the general direction of Regulus. However, on the 21st it stands still, then starts to move in the opposite direction – westward. This is called “retrograde” motion and is caused by our overtaking it as both planets orbit the Sun.

Here are the key numbers and dates for this apparition of Mars, according to Sky and Telescope magazine:

  • Mars will appear larger than 10 seconds in diameter from December through March – that’s big enough to see some features in a backyard telescope.
  • In late January it comes closest but will still appear to be only 14.1 arc seconds in diameter at its largest – on a really good year, such as 2018, it will appear to be over 24 seconds in diameter .
  • In 2012 – when we get another close look – it will actually be a tad smaller at its best because it will be a little farther away.

What should you be able to see? Frankly, not that much. But it’s still fun to try. With a good telescope and good astronomical “seeing” conditions, you should be able to make out some features on Mars such as the northern polar cap, and large, irregular olive drab splotches that stand out against an orange background.

Jupiter’s close encounter with Neptune

Jupiter has had three close encounters with Neptune this year – this is the last. (To read about the first, see this post.)  While Mars is a target for late evening viewing, Jupiter needs to be seen early in the evening, for it sets earlier each night. With a telescope you can start viewing 45 minutes after sunset.

You can find Neptune reasonably near it – using a telescope – all month, but it will be closest during the few nights around December 21st. This changes rapidly, so even if you are a few days either way Neptune quickly gets lost in the background of stars of similar brightness. But on or near December 21 it will be less than one degree away from Jupiter and you should be able to fit both planets in the same field of view if you are using  a low-power, wide-field eyepiece. But keep in mind, at magnitude 8, Neptune is significantly dimmer than Jupiter’s moons.

As a bonus, the crescent Moon is just five degrees away, above the two planets, on December 21. Here’s a finder chart for December 21, 2009 showing Jupiter and Neptune as seen in a low-power telescope view with the image flipped left-to-right, which is what you will see when using a telescope thathas a diagonal mirror. With a reflecting telescope the image also will be flipped AND upside down.

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

To download a printer friendly version of the preceding chart, go here.

And Saturn?

The ringed planet – and yes, it’s rings are tilted to us now in such a way that they are again easy to see in a small telescope – is an early morning treat in December.  Although it rises just before midnight at the end of month, it’s not above the horizon until nearly 4 am at the outset. My advice – get up early – about two hours before sunrise. Our chart’s for that time at mid-month and at that time Saturn is well placed in the southeast for telescopic observation. It is one of the brightest “stars” in that section of the sky and easy to pick out with the naked eye.

Click image for larger version. Starry Nights Pro screen shot with annotations added.

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

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