September 2004 Sky from the Keeble Observatory
Cassini has been orbiting Saturn for two months, and has already
begun to return impressive data on the ringed planet's many satellites.
Phoebe, the most distant of Saturn's "major" moons, was
imaged while the probe was still inbound. Long-range images of Titan
have begun to penetrate its smoggy atmosphere. Two previously unknown
moons have been discovered, too small to be seen by earth-based
Titan is the only satellite in the solar system with a substantial
atmosphere. Two Voyager probes in the 1980s managed no better than
to confirm that the atmosphere was dense and hazy ... nothing could
be seen of the surface. The atmosphere is mostly nitrogen, which
is also true of Earth's atmosphere, but there's no free oxygen on
Titan. It is also extremely cold, fortunately so, since the moon
is not massive enough to hold a warm atmosphere. The haze in the
atmosphere seems to be hydrocarbon "smog" ... and radar
reflected from the surface tells us that there may be pools of liquid
hydrocarbon on Titan. Think lakes of gasoline! Initial images of
Titan at wavelengths not absorbed by the smog have given a preliminary
view of the surface, which will be much improved when Cassini passes
within a few thousand miles of the surface in December. A separate
probe, Huygens, will penetrate that atmosphere and parachute to
the surface. See for yourself at http://saturn.jpl.nasa.gov/home/index.html.
The newly-discovered moons, as yet unnamed, are a mere 3 and 4
kilometers (2 and 2 ½ miles) in diameter, making them substantially
smaller than any previously identified satellites. The smallest
previously known were about 20 kilometers in diameter. The existence
of these small satellites has been used to argue that there are
fewer small comets in the outer solar system than many had believed.
The reasoning is that over the 4.5 billion year age of the solar
system, house-sized comets would have blasted small satellites into
rubble, which would have become part of the rings. Since these moons
are still there, perhaps there aren't as many small comets. Cassini
researchers will continue to look for evidence of more small moons,
particularly in the several gaps in the ring plane.
Lunar phases for September: Last Quarter on the 5th; New Moon on
the 14th; First Quarter on the 21st; Full Moon on the 28th.
Evening planet watching will continue to disappoint! Mars and Jupiter
are essentially lost in the Sun's glare, Uranus and Neptune can
only be seen with a modest telescope. Morning sky-watchers will
have a better array of planets. Mercury, Venus, and Saturn all grace
the eastern sky at sunrise. Saturn rises about 3 hours before the
Sun, followed an hour later by Venus. These will both be very bright
... Venus will probably be the brightest object in that direction.
Mercury lies below Venus, and should also be bright. Look for all
three to gain height above the horizon as the month goes on.
Two hours after sunset finds Cygnus, the Swan, directly overhead.
Its brightest star, Deneb, is just to the north of zenith. Cygnus
marks the northeast to southwest plane of our Milky Way Galaxy,
and also lies in the direction towards which our entire solar system
is moving as we orbit the distant galactic center.
To the west of zenith lies Vega, in Lyra. Binoculars should enable
you, on a clear moonless night, to pick out the faint Ring Nebula,
also in Lyra. Also, seeing doesn't have to be perfect for binoculars
or a small telescope to resolve the "double-double" -
the modestly bright star next to Vega - as a pair of close binaries.
Hercules, lies about 30 further degrees to the west. You should
still be able to see the globular cluster M13 in Hercules - it will
look like a faint dandelion puff, composed of perhaps a million
From zenith towards the east, your line of sight moves out of the
plane of the galaxy. The largely open sky is marked with the large
but rather faint "great square" of Pegasus. Low to the
northeast you'll see the familiar, irregular W shape of Cassiopeia.
To the right, at about the same angle from the horizon, you should
be able to see the faint "smudge" of the Andromeda galaxy,
even without a telescope. It's best seen in a clear, moonless sky.
Light from that galaxy has taken about 2 million years to reach
your eyes, making it the most distant "naked eye" object
For your own monthly star chart, you can direct your web browser
You will find extensive descriptions of what's worth looking for,
and you can download and print a single copy for your personal use.