December 2007 Sky from the Keeble Observatory
Mars will be at closest approach on this orbital cycle on the 18th of
December – a good chance to see it with binoculars or a small telescope. Last August
I received myriad emails with questions about Mars appearing “larger than the full
moon.” These were, unfortunately, linked to an urban legend that popped up in 2003
when Mars was at closest approach in August. For the record – you will never see
Mars appear that large unless you’re in a spaceship or using a telescope! The closest
Mars gets to Earth is a little under 35 million miles.
It will be at opposition on the 24th, rising at sunset. The two events
are not coincident, because neither our orbit nor Mars’ is a perfect circle. They
are both ellipses, and their long axes are not aligned. Both events occur approximately
every 26 months, though not quite in synchrony, which is why we see Mars probes
launched at the same interval, timing their arrival with the lowest energy expenditure
to get from here to there.
Lunar phases for December: (Note: all times are Eastern Standard) Last Quarter
on the 1st, at 7:44 am. New Moon on the 9th, at 12:40 pm;
First Quarter on the 17th, at 5:18 am; Full Moon on the 23rd,
at 8:16 pm. We get another Last Quarter moon on the 31st, at 2:51 am.
If you were on the west coast, this would happen on the 1st of January!
Predawn planet watchers will still have some good targets, though they’ll all be
getting lower as the month advances, and some will disappear into the Sun’s glare.
Early in the month, at sunrise, Venus is still the brightest thing in the sky, about
37 degrees above the south-southeast horizon. It’s close to the bright star Spica
in Virgo, but much brighter. Saturn is high to the south-southwest, about 60 degrees
up and near Regulus in Leo. Mars is to the west at about 28 degrees altitude, below
Castor and Pollux in Gemini.
Late in December, Venus will appear closer to the Sun, only 28 degrees above the
horizon at sunrise, and now near Antares, in Scorpio. The general “drift” of the
planets against the background stars is toward the east, with those planets closer
to the Sun showing the greatest apparent motion. Saturn has drifted to the east,
but not nearly as much as Venus – it’s ten times farther from the Sun than we are.
Look for it still to the south-southeast, but now only about 37 degrees above the
horizon and still near Regulus.
Early evening planet watchers will have to content themselves with Jupiter low to
the southwest at the beginning of the month, only about 12 degrees above the horizon
at sunset. The good news is that Mars rises earlier and earlier – about an hour
after sunset early in the month and about an hour after sunset by the new year.
Mercury will return to the early evening skies early next year.
Looking overhead at mid-month, about three hours after sunset, finds the constellation
Andromeda at zenith. It’s not an impressive or terribly bright asterism, but is
noted for the presence of the Andromeda Galaxy. Two million years ago the light
you see from this relatively nearby galaxy, much like our own, left to come to Earth.
We see our own galaxy in cross section as the faintly luminous Milky Way, stretching
from east to west, with a distinct bow towards the north. The stars making up this
band are typically hundreds to thousands of light years away – a factor of over
a thousand smaller than the distance to Andromeda.
The constellation Cassiopeia is to the north, in the plane of the Milky Way. It
looks like a crooked M. To the west-northwest, Cygnus the Swan now looks like its
other namesake, the Northern Cross. Deneb is the bright star at the top of the cross,
about 40 degrees from the horizon. To the northwest is Vega, at about 18 degrees,
and Altair is a little lower and to the west. When these were high in the sky, we
called them the Summer Triangle. Now we bid them adieu until late spring.
Rising to the east is Orion, which will dominate the winter starscape. Above Orion
is the familiar cluster of the Pleiades, about 55 degrees from the horizon and climbing.
A special note, that the Geminid meteor shower should peak early in the morning
of the 14th. For several days around that date, you can expect to see
up to 75 “shooting stars” per hour. For best viewing, get to a dark site away from
For your own monthly star chart, you can direct your web browser to
http://www.skymaps.com. You will find extensive descriptions of what's worth
looking for, and you can download and print a single copy for your personal use.