December 2006 Sky from the Keeble Observatory
It’s hard to say goodbye, but sometimes we have no choice. The Mars Global Surveyor,
which has been orbiting the Red Planet since 1997 September 11 (well before that
day took on its current meaning in our calendar) has fallen silent. The last communication
with the probe was on 2 November. What has apparently happened is that the solar
array can no longer pivot into the necessary orientation to generate power sufficient
to operate the instruments and radio transmitter.
This has been the longest continuous robotic mission to Mars. Launched in 1996,
in the nine years since entering orbit, the spacecraft has returned nearly a quarter
million images. These have led to the discovery that at least some of the erosion
features on Mars are relatively recent. Its laser altimeter has measured precisely
the global topography of Mars. Its magnetometer has discovered evidence for remnants
of what may have once been a global magnetic field, which Mars currently lacks.
The mineral mapping experiment, primarily an infrared spectrometer, identified the
presence of hematite in several areas. On Earth, hematite forms usually under wet
conditions - so, this information was used to target the two Mars rovers to their
current sites. We should also note that the entire 10 year mission has cost far
less than the price tag of a single space shuttle flight.
For more about the Mars Global Surveyor, direct your web browser to
Lunar phases for December: Full Moon at 7:25 pm, on the 4th; Last Quarter on the
12th, at 9:32 am; New Moon on the 20th, at 9:01 am, and First Quarter on the 27th,
at 9:48 am.
Saturn rises progressively earlier and earlier as the month advances. Recall that
last month we didn’t see it until after midnight, it will rise to the east-northeast
around 11:00 pm early in the month, and as early as 8:30 by the time the calendar
rolls over to January and 2007. Venus has returned to the evening sky, and can be
seen low to the southwest at sunset early in December, about 12 degrees above the
horizon by month’s end. Unfortunately, that’s about it for evening planets!
The early morning is more productive, including some interesting conjunctions. Saturn
is high (about 50 degrees) to the southwest at sunrise, near the bright star Regulus
in Leo. Later in the month, you’ll find Saturn still near Regulus, but at sunrise
it will be to the west and only 30 degrees from the horizon. To the east-southeast,
Mercury, Mars, and Jupiter all rise before the Sun. Early in the month, look for
them spaced at roughly 5 degree intervals – Jupiter at 5 degrees, Mars at 10 degrees,
and Mercury at 15. But, as Jupiter and Mars continue to climb into the predawn sky,
Mercury is already cycling back towards the Sun. They’ll all be within a degree
or so on the 10th and 11th, with Mercury and Jupiter showing only a third of a degree
separation on the early morning of the 10th.
Looking overhead about 3 hours after sunset at mid month, we find the Milky Way
nearly bisecting the sky from east to west, bowed slightly to the north, so that
the direction toward zenith misses the faint band of luminosity. (You’ll only get
a good view of our home Galaxy if you can get away from city lights – the same advise
for seeing the Geminid meteor shower around the same time frame.) The Andromeda
Galaxy is high to the northeast, only 10 degrees from zenith. To the north, Cassiopeia
looks like a crooked M. Turn to the north northwest – Cygnus now clearly looks like
the “northern cross” instead of a fancied Swan. Below and to the right of Cygnus,
you should still be able to pick out the bright star Vega. The eastern horizon is
busy, with Orion rising, following Taurus. In Taurus we see the familiar asterism
of the Pleiades, also known as the “seven sisters.” It’s even more familiar to drivers
of Subaru vehicles – it’s on the grill! (Subaru is the Japanese name for this stellar
grouping.) It’s actually an open cluster of several hundred stars, about 400 light
years distant. This cluster is much younger than the Sun, only about 10 million
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.