November 2012 Sky from the Keeble Observatory
Our last column was in September – doesn’t time fly when we’re having fun? I suppose
I could blame the lack of an October column on all the robo-calls leading up to
the election, but the reality is that it just slipped by me!
Planets have been in the science news of late, so let’s see what’s new.
Curiosity continues to perform its job of surface exploration on Mars. It hasn’t
moved terribly far, since it keeps stopping to do science. They’ve analyzed soil
samples (similar to terrestrial basalts – i.e. volcanic rock from places like Hawaii),
tested the atmosphere for methane (not much, if any), and measured the isotope ratios
in atmospheric gases. They’ve found that slightly more of heavy isotopes of carbon
are present in the carbon dioxide than in terrestrial CO2. This suggests
that the currently very thin atmosphere (about 1% the density of our atmosphere)
is the remnant of one once denser, and that the loss of gas was from the top of
the atmosphere rather than being trapped chemically in the solid surface, because
the lighter molecules would be more likely to escape at high altitudes.
The Cassini probe at Saturn detected a huge “belch” of methane in a storm which
carried warm gas from the interior to the cloud layers. This gas was several hundred
degrees warmer than the clouds it penetrated.
Planets in the Alpha Centauri system are a long popular trope in science fiction
– I can’t tell you how many novels I’ve read which include them! Now we know of
at least one! A roughly Earth sized planet is orbiting Alpha Centauri A, an essentially
Sun like star only 4 light years away. Before you pack your bags for a visit, it’s
extremely close to its star, and the surface is likely to be molten rock rather
Last August, observers using the Kepler probe announced the discovery of a pair
of planets orbiting a pair of stars! Kepler 47 is a binary system which includes
two stars. One is a bit cooler than the Sun, the other is much cooler and smaller.
One of the two planets orbits in the so-called habitable zone, i.e. where the temperature
would be close to what we find on Earth. However, these planets are probably more
like Neptune than Earth.
Next month we’ll talk about how we detect these planets, and how we think we know
how big they are.
Lunar phases for November: Last Quarter on the 6th, at 7:36 pm;
New Moon on the 13th, at 5:08 pm (There will be a total solar eclipse,
but it won’t be visible here. Catch a flight to Australia, New Zealand, and New
Caledonia if you want to see it!); First Quarter on the 20th, at 9:31
am; Full Moon on the 28th, at 9:46 am (There will be a penumbral lunar
eclipse, but you won’t see it in daylight!).
Evening planet watchers will have to content themselves with following Jupiter,
which rises to the east about 7:00. It will be bright to the south after midnight,
about 70 degrees above the horizon. Venus and Saturn rise to the east before sunrise,
Venus will be about 30 degrees above the horizon, and will be the brightest object
until the Sun clears the horizon. It rises about an hour before Saturn, so Saturn
will be lower and much fainter, if you can pick it out of the predawn twilight.
Saturn will rise a little earlier each day, so expect it closer and closer to Venus
as the month advances. Mercury joins them by month’s end.
Looking overhead at mid-month, about two hours after sunset you will find the Milky
Way dividing the sky from northeast to southwest. Deneb and Vega are the two bright
stars to the west of zenith, with Altair to the southwest marking out a rich triangle.
Near Vega, a clear night and steady hand with binoculars may enable you to see the
Ring Nebula. This is an example of what will happen to our own Sun in another five
billion years … as the fuel in the core is used up, the outer layers will eventually
be expelled into an expanding planetary nebula. To the east of zenith, look for
the Andromeda Galaxy, a faint smudge to the naked eye. This is actually a galaxy
much like our own, over 100 billion stars yet dimmed by its vast distance of some
2 million light years. Even though it is the most distant object visible without
a telescope, it is close by on the cosmic scale of things.
Deneb marks the “tail” of the constellation Cygnus. The “head” is a faint binary
called Alberio, which is one of the most beautiful pairs you’ll see. With a small
telescope, one star glows a brilliant blue while the other is bright orange. Cygnus
lies in the general direction of the Sun’s orbit around the center of the galaxy,
which lies in the direction of Sagittarius, which is just setting on the southwest
Just rising to the east is bright Aldebaran, in the constellation Taurus. This is
a harbinger of coming winter. By month’s end we will see Orion rising at this hour.