November 2005 Sky from the Keeble Observatory
The early evening is highlighted by our two nearest planetary neighbors. At the
onset of twilight, you’ll notice a very bright “star” to the southwest. That’s Venus,
catching up to us as it orbits closer to the Sun than we do, and hence moves faster.
The brilliance is for two reasons: first, it’s getting closer. Second, it is shrouded
in clouds, which reflect most of the visible light striking the planet. That Venus
is almost the same size as Earth and covered in clouds once led astronomers to believe
that conditions there would be somewhat like on Earth, but perhaps a bit warmer.
Steamy jungles and dinosaurs were common fare in pulp science fiction, not to mention
fair maiden princesses ready to be rescued by an intrepid hero from your home planet.
We now know otherwise. The clouds are not water, rather they are sulfuric acid.
“A bit warmer” turns out to be 750 K! The dense atmosphere is mostly carbon dioxide,
and about 90 times as dense as our own air. CO2, known to be a factor in global
warming on Earth, is responsible for a “runaway greenhouse effect” on Venus.
To the east, you’ll see Mars rising a few minutes earlier each evening. Directly
opposite the Sun on the 6th, you’ll see this bright red light climb higher and higher
as the month progresses. We’ve nearly caught up to Mars as I write this, and we’ll
pass it on the inside lane, much as Venus is catching up to us, and will eventually
pass us and move from the evening to the morning sky.
Mars is only a third the size of Earth, so it cannot hold on to a dense atmosphere.
Even though its thin CO2 atmosphere keeps it warmer than it would be without, that
still leaves Mars a very cold planet. The permanently frozen polar caps are believed
to contain most of the water on the planet, with deposits of frozen carbon dioxide
(dry ice) providing the seasonal variations. The pressure at the surface is so low,
less than 1% that on Earth, that liquid surface water is not possible. Even at the
cold temperatures found there, liquid water would boil away quickly.
Only on Earth among the three do we find conditions for liquid water! It’s sort
of like Goldilocks: Venus is too hot, Mars is too cold. Earth is just right!
Lunar phases for November: New Moon at 8:25 pm, on the 1st; First Quarter on the
8th, at 8:57 pm; Full Moon on the 15th, at 7:57 pm; and Last Quarter on the 23rd
at 5:11 pm.
Early morning sky watchers will still get to follow Mars – look for a bright red
“star” to the southwest, about where Venus was the previous evening. Jupiter rises
about an hour before sunrise by mid-month, stretching that to 2 hours by the end
of November. Mercury will return to the morning sky at the end of the month. Look
for it about half-way to the sunrise point from Jupiter.
Evening skywatchers will also have a chance to see Mercury, but low on the southwestern
horizon at the beginning of the month. On the 3rd it reaches its greatest eastern
angular separation from the Sun, but the plane of its orbit makes a very shallow
angle to the horizon at sunset. Mars reaches opposition on the 6th, rising about
4 minutes earlier each day. By month’s end, Mars rises an hour before sunset, so
it will be visible until about an hour before sunrise.
About two hours after sunset at mid-month, an overhead look finds the Milky Way
dividing the sky from northeast to southwest. Deneb, in Cygnus, is about 20 degrees
northwest from zenith. Another 20 degrees in that direction brings your line of
sight to Vega, in Lyra. Another 20 degrees and you’re looking at the constellation
Hercules. Binoculars early in the month, near New Moon, should allow you to find
several deep sky objects in Hercules, including a fairly large globular cluster.
If we go back to Deneb, and shift our line of sight toward the northeast, we’ll
find the familiar “M” shape of Cassiopeia, tipped on its side about 55 degrees off
the horizon. Follow the bottom “leg” of the M toward the right about 15 degrees,
and you’ll find the Andromeda Galaxy. It’s not bright, it’s somewhat diffuse, so
your best bet is on a moonless night.
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.