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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.

December Events – a brilliant crescent Venus, Jupiter, and moon-drenched meteors

Venus – brilliant shortly after sunset to southwest

Chart shows position of Venus, roughly two fists (18 degrees) above the southwest horizon for much of December. During the last half of the month it will move closer to the Sun - and thus closer to the horizon half an hour after Sunset and by the end of the month will only be about 8 degrees high.  Vega and Altair will be much dimmer, but should show within about 45 minutes after sunset. (Created from Starry Nights Pro screen shot.)

Chart shows position of Venus, roughly two fists (18 degrees) above the southwest horizon, for much of December. During the last half of the month it will move closer to the Sun – and thus closer to the horizon half an hour after sunset and by the end of the month will only be about 8 degrees high. Vega and Altair will be much dimmer, but should show within about 45 minutes after sunset. (Created from Starry Nights Pro screen shot.)

For telescope users – and maybe even those with binoculars – Venus does a gorgeous job of showing off its phases this month as it shrinks and grows at the same time.  For all of us, with telescope or not, it’s a brilliant “evening star” dominating the southwestern sky about half an hour after sunset.

Galileo was the first to see this and it was part of his argument for a Sun-centered solar system. Like Galileo, if you really want to see the phases you need a telescope, though near the end of the month you may be able to detect its thin crescent with good binoculars held very steady.

You won’t have any trouble finding it.  It’s that most brilliant “star” about 18 degrees – a little less than  two fists held at arm’s length – above the southwestern horizon half an hour after sunset.  It shrinks in terms of the amount of its disc that is lit. At the start of December 2013 about one third of the disc is lit – by the end of the month this will drop to just 5 percent. Amazingly, it stays almost the same brightness all month – in fact, this is the time it is at its most brilliant. Why? Because it is overtaking Earth in its orbit and in January will pass between us and the Sun – a sort of “new moon” phase, then become visible in the morning sky. ( When Venus is in its “full moon” phase it is farthest from us, so even though nearly the entire disc is lit, it does not appear nearly as bright.)

Positions of inner planets in mid-December, 2013. All are moving counter clockwise and Venus is about to overtake the Earth, passing between us and the Sun.

Positions of inner planets in mid-December, 2013. All are moving counter clockwise and Venus is about to overtake the Earth, passing between us and the Sun. Mars is positioned to be seen in our morning sky and Mercury is visible at the start of the month before dawn, but is pretty much lost most of the month in the glare of the Sun.

And about the growing Venus? Well, as it gets nearer to us it also appears larger. At the start of the month it’s disc about 38 seconds in diameter – by  the end of the month it is nearly a full minute of arc in diameter. To give you an idea what a minute of arc is, stand on the goal line of a football field and have a friend go down to the 10 yard line at the othe end and hold up a quarter? Can you see it? You may be able to if you have excellent vision.

On the other hand, a quarter held nine feet away is roughly the size of the full Moon – or Sun – in our sky – about 30 minutes of arc, or 30 times larger than Venus will appear in a telescope at the end of the month.

If you do go looking for the Venus crescent with binoculars or a small telescope, go out early. Locate  it while still in twilight, about half an hour after sunset. There’s less glare then and so it is easier to see the form. Later, as it gets fully dark, Venus is so bright you may find detecting its crescent difficult even in a telescope.

Jupiter – very bright as it rises in the east a couple hours after sunset

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

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

So is Venus the only special show in in our December skies this year? No. If you wait until “prime time” – about 8 pm – you will see a very bright “star” rising in the east. This is Jupiter, which by the end of the month starts coming up right after sunset.  Once it’s fairly high in the sky it makes a good target for binoculars. Its disc won’t be quite as large as Venus, but it does have four bright Moons and you can almost always find one or two of them with binoculars – sometimes three or even four.  Galileo did it four hundred years ago with a telescope that certainly wasn’t as good as most modern binoculars, but was a bit more powerful. Again, you need to hold your binoculars steady and focus them carefully.

Geminids – nice, but they will be drowned out some by moonlight

We also have the best meteor shower of the year putting in its annual appearance in December – the Geminids. Unfortunaetly, this year it will have to compete with the nearly full Moon. Still, Geminid meteors tend to be slow and quite bright, so even with the Moon you should see some. The shower is forecast to peak just after midnight (EDT) on Saturday morning, December 14th. That means late on the night of December 13th – hmmm, Friday, the thirteenth – should be good for seeing Geminids and the best views  will come in the very early morning hours of Saturday when the Moon is low in the west and the shower’s radiant point – in Gemini near Jupiter – is high in the sky.

Solstice – December 21, a good reason to celebrate

You need not be a Druid to celebrate this just after midnight EDT on December 21, 2013.  For northern hemisphere observers the winter solstice means the Sun has stopped running south and is turning around and heading back north. Of course it will take a few months before it’s warming rays change our weather much, but the fact that it is heading back north is a good sign.

It’s hard to imagine just how much that would mean to people living off the land and dependent on the seasons. Even in my warm home I am  cheered by the change, Every morning when I take the dogs out I see the Sun rising on the southeast horizon. At this time of year it appears to stand still for a week or so – but by the end of the month the northward movement becomes noticeable as I mark its path by the trunks of the bare trees I see it through. Of course for those of you in the southern hemisphere this marks the start of summer.

Christmas Star – it’s in your heart, but either Venus or Jupiter will be a nice reminder

In December I frequently get asked about the Christmas Star and while competing scientific theories have abounded about it for centuries, in the final analysis it is a Christmas myth that you can choose to believe, or not believe. Various scientific explanations – informed guesses – range from certain gatherings of planets, to a comet or super nova. Part of the problem is we don’t know the date – not even the year – Jesus of Nazareth was born, so various astronomical  – and astrological – possibilities exist depending on the date chosen. Me, I just take any bright star that’s visible and treat it as  a symbolic Christmas Star. This year we have Venus in the west for a couple hours after sunset – and by the time it sets we have a very bright Jupiter rising in the east.

Events December 2012: Mercury, Meteor Shower, Dwarf Planet, Jupiter, and more!

geminids

OK, so the meteor shower might be a snow shower, it being December and all, but we also get  an especially nice apparition of Mercury with Saturn and Venus guiding us to the elusive planet. And if that’s not enough, we have the ever reliable Winter Solstice – start beating the drums to bring the Sun back out way, please – and the King himself, Jupiter dominating an already brilliant eastern evening sky  plus a nice asteroid pass to accompany a not-quite-as-bright Dwarf Planet – you know, one of those Pluto-like things! Whew – out of breath just thinking about it all.

Here are the links to one  event at a time if you want to jump straight to the details.

Geminid Meteor Spectacular – December 13-14

First, please meditate on this: Ask someone who is 50 miles away to strike a wooden kitchen match. Can you see it? Of course not. But that’s what’s going on when you see a meteor flash across the sky! Chances are it is from a particle about the size of the head of a kitchen match – or smaller –  and it is burning up as it hits the atmosphere above you travelling at up to 100 times faster than a rifle bullet.The result? A very, very bright “match.”

And now the Geminids – As you may know, I really don’t like that word “shower.” It builds expectations out of proportion usually, but if you have clear skies on the night of December 13-14th it’s worth digging that folding  chaise lounge out of storage, wrapping yourself in a sleeping bag – with binoculars and hot beverage handy – and staring up at those wonderful bright stars of winter waiting for some to “fall.”  Hey, if you have an Iphone or Ipad there’s an app for this – no kidding – you can record what you see and ship it off to NASA, thus contributing to scientific research –  all quite painlessly. (Go here for details.)

Oh – and this is the time of new Moon, so the Moon won’t be present to upstage the show with its bright light. The official word goes something like this – expect “about 120 meteors visible per hour for an observer at a dark sky site late on the peak night.”  That’s how Sky and Telescope puts it and those folks certainly know what they’re talking about, but in many nights of meteor watching I’ve never seen anything close to 120 per hour. When that’s the forecast I figure I have a good chance of seeing 20-30 an hour and believe me, that’s a real treat.  Maybe your skies are darker than mine, maybe your eyes are better, and maybe you’re more patient – so maybe you’ll see 120. Me – I will be delighted with a meteor every two-to-three minutes –  if not a quite a shower, that’s a  snappy snow flurry!

So where do you want to look? Up! Any part of the sky  can produce meteors, but if you trace their trails backward you will see they all emerge from the same general section of sky near Castor, the slightly dimmer Gemini twin.  Since they appear to radiate from this area of sky the most meteors will be visible when it is high overhead – and looking in that general direction is a good idea. Here’s a chart for 1:46 am ET -when Castor is at its highest – on the morning of December 14.

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

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

So does that mean you have to wait until  early morning to enjoy the Geminids? No! But it makes sense that if the radian point is near the eastern horizon – which it is a couple hours after sunset – then you cut your chances of seeing a meteor in half – which still means a very respectable number of meteors.  The higher the radiant point the more chance you have of seeing more meteors. But then, you can’t watch the whole sky at once – even if you have remarkably clear horizons – and one thing about meteors – they are very fast and there’s no instant replay. Blink – or be looking the wrong way – and you may hear the ooohhs and aaaahhs of companions, but you will most likely not see what they saw.

Most meteor showers are the result of the Earth passing through a trail of comet dust  – think of “Pigpen” in “Peanuts” and you get the idea of comets leaving a trail of dust. But not the Geminids. They’re something of a mystery, but the current theory is that they come from a maverick asteroid. To read all about it, go here.

Hey – why not do the observing right?  Go out about 2 am and enjoy a couple hours of meteor watching, then shift your focus to the eastern horizon where Saturnn, Venus, and eventually Mercury will put in an appearance – quite a show, really.

Mercury – an early month, early morning stage appearance with Saturn and Venus

Mercury  reaches longest elongation – distance from the Sun –  on December 4th and while it will be well-placed for another couple weeks, you need to grab the little winged messenger when you can. It pops above the horizon six times a year – three in the morning sky and three in the evening sky, but not all pops are created equal. This happens to be its best appearance for 2012.  As a bonus, brilliant Venus will act as a guide. The two planets will be closest on December 9th when you should be able to squeeze them both into the same low-power binocular field of view. But all month they will be close enough for Venus to help in finding Mercury and Saturn will be visible a bit above Venus.

Of the three, Venus will absolutely dominate in brightness at magnitude -3.9. But Mercury on December 4th will be just a tad dimmer than the brightest star we can see (roughly -0.5) and Saturn is no slouch at 0.65 – and they’re in the southeast with two bright guidepost stars, Arcturus and Spica. Here’s what to expect.

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

December 11th isn’t so shabby either because we get a crescent Moon in the picture as well, though both Venus and Mercury have dropped  down a bit, you should still be able to find them both. Venus will be easy. Mercury – well, you may want to use binoculars, though it should still be visible to the naked eye if you have clear skies – and, of course, an unobstructed eastern horizon. It’s only about half a fist above the horizon at this point.

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

The Winter Solstice – Sure it happens every year but it always seems special – December 21

What’s so special about the Winter Solstice? Well, for me it’s a reminder that all life – you and I, plus every animal and plant on this tiny planet depend on the Sun. The Winter Solstice – as seen from the Northern Hemisphere –  reminds me of this because on the morning of December 21 the Sun will rise as far south as it gets. In the next few days it will start inching it’s way back north and that is certainly a good sign. Sure, our seasons lag behind the sky a bit. The worst of the winter weather is yet to come. But the fact that the Sun is on its way back is certainly an encouraging sign. More primitive societies that were in better sync with the natural rhythms of the sky, celebrated this time of year and with darned good reason.

Ceres is Ceres – but you can call it a dwarf planet

“Dwarf planet” was the category astronomers agreed upon in 2006 to fit objects that are big enough to be round, but too small to have cleared the area of their orbit of other objects. That’s what Ceres is and so is Pluto, and three other known objects.  It amazed me that this rather technical decision (I have greatly over-simplified the definition) caused such a stir because it demoted Pluto from planet to dwarf planet. These are simply classifications and in astronomy over time classifications get kind of messy. I mean, stars in the 19th Century  were classified in a nice alphabetical list by their spectra – but then we kept learning more and the list got screwed around  to anything but alphabetical: OBAFGKMLT. What’s more, our Sun – and many other stars that are among the larger ones, is called a “dwarf star!” Oh my – now that sounds illogical, if not offensive.

Oh – and Ceres, the first asteroid discovered (1802) – and largest (952km) – is still often referred to as an “asteroid” because it is a dwarf planet inside the orbit of Neptune where we usually find asteroids – arghhhhhhh! See why I want to just call it Ceres and be done with the naming thing ?  😉

Do click onthis for the full-size image - that's really Vesta as imaged by Dawn, but essentially this is an artists view of what it must have looked like as the Spacecraft orbited the asteroid.

Do click on this for the full-size image – that’s really Vesta as imaged by Dawn, but essentially this is an artists view of what it must have looked like as the Spacecraft orbited the asteroid.  (We didn’t send anyone along in another spaceship to take pictures of the two!)

But Ceres – and even brighter Vesta – have been the subject of an extensive examination conducted by the NASA  “Dawn” spacecraft.  It has spent a year examining Vesta and is now on its was to get up close and personal with Ceres. But you can beta it to it – you can see both Cere and Vesta from your backyard this month with nothing more than binoculars, a few charts, and some determination. Of course your view will be a bit less detailed. The two will appear as stars just below naked-eye visibility. And although it’s about half the size, Vesta is the brightest because it happens to be made of – or have on it’s surface – shinier material.

This is an excellent opportunity for you to test your skill with binoculars. This month they will both look like sixth magnitude stars and thus be easily seen in binoculars – but I won’t underestimate the challenge. The good news is they are well placed near bright, familiar stars and the brilliant planet Jupiter in the evening eastern sky. That makes it easy to find the general area in which to search. The bad news is there are lots of stars up there – especially when you look with binoculars – so you need to really study the charts before you go outside, then do  very careful observing. If you find it one night, it’s  fun to look again in a few days, or even a week or two – because they do change positions rather rapidly while the stars, of course, stay put.

Go here to get a printable chart of the Path of Ceres and Vesta over the next few months.

Now print this chart to use to mark your observations of Ceres and Vesta over the same period.  It’s a chart of the same area of sky covered by the previous chart, but with the position of Ceres and Vesta shown only for December 9, 2012 as viewed from mid-northern latitudes about four hours after sunset. However, while the orientation changes somewhat by date and time, it should serve to track Ceres and Vesta for December and January. Magnitudes of a few selected objects are given in parenthesis to help identify Ceres and Vesta. Before going outside to make your observation, study the chart and determine where you think Ceres and Vesta should be that night.

And as you look at Vesta, get this picture in your mind’s eye – and as you will see at the end, Ceres look a bit different, but how different – well, we’ll see when Dawn gets there!

And here’s the best view we have of Ceres as seen by the Hubble Space Telescope.

Images of the Asteroid Ceres As It Rotates One Quarter
Source: Hubblesite.org

Jupiter – let’s not forget the king of the planets

As some wag commented, our Solar Systems consist of the Sun, Jupiter, and some debris!

It is big – and only Venus outshines it, and yes, with careful viewing you can see one or more of the four Galilean moons using only binoculars. The key is to hold them steady and observe – don’t just look.  A “look” is what most people tend to do at first – that is, they hold the binoculars up and if, in 10 seconds or so, they have not seen the moons, they give up. That is not observing. To observe you need to look for at least a solid minute. That won’t guarantee you see the moons, but just taking a quick look can mean you easily miss them.

They may all be on one side of the planet and they constantly change their relationship with the planet and one another so that even with binoculars you can notice the difference over the course of a few hours. They will look like tiny stars, they will be close to the planet, and they will be roughly in a straight line that passes through the planet’s equator. This line will be pointing upward as the planet rises, level off when it’s near the mid-point of its arc across the sky, and be slanting down as it heads for the western hprizon.

The best way to prepare yourself for what to see – to check to see if you are seeing the right thing – is to go to the Sky and Telescope web site and use the javascript simulator there for your date and hour.  To do that, go here . With binoculars you want the right-side up view. With small telescopes it is much easier, of course, to see these Moons, but a telescope will change the orientation and this script allows you to change that orientation to match your telescope’s view. Here’s a typical example of what you will see.

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