• Choose a month

  • 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.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: