Keeble Observatory
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 http://mars.jpl.nasa.gov/mgs/.
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 years old!
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.
Copyright 2006
George Spagna