February 2005 Sky from the Keeble Observatory
After seven years hitching a ride on the Cassini spacecraft, the Huygens probe took
center stage and delivered a nearly flawless performance. Omission of commands to
activate one of the radio receivers on Cassini meant that about half the data were
irretrievably lost. Even so, the remaining data are giving us our first close up
look at the atmosphere and surface of Titan. Saturn's largest moon is the only satellite
in the solar system with a substantial atmosphere. Methane haze in that nitrogen
atmosphere had kept the surface shrouded in mystery ... until Huygens arrived.
One of the strangest places in the solar system, it was amazing to see how familiar
the surface looks. River channels carved through low hills, leading to large lakes.
Low lying fog clings to the shore line in places. Islands poke out of the sea.
(Image courtesy of European Space Agency, National Aeronautics and Space Administration,
and the Lunar and Planetary Lab at the University of Arizona.)
Huygens parachuted to a soft landing near one of the lakes, landing on a surface
the consistency of wet sand. Pictures from the surface show small "boulders,"
which appear to have been tossed and smoothed in flowing liquid. Researchers claim
evidence that it has "rained" recently.
But this is not familiar territory! The rain, rivers, and lakes are liquid methane,
at about 200 degrees below zero, and the fog is also methane. There does not appear
to be any standing liquid at the moment, but the consistency of the surface suggests
that the liquid lies just below in the "sand." The boulders and sand are
most likely frozen water ice! We need to be cautious about drawing too many conclusions
- we've seen only a tiny fraction of Titan!
Cassini continues it orbital examination of Saturn and her moons. Huygens' batteries
are long since expired, and it will be decades (at best) before we can get another
look at the surface of Titan. Lost data notwithstanding, there will be much to learn
from the current mission.
Lunar phases for February: Last Quarter on the 2nd, at 2:27 am; New Moon at 5:28
pm, on the 8th; First Quarter on the 15th, at 7:16 pm; Full Moon on the 23rd, at
Evening planet watchers will have Saturn available all month. At sunset early in
the month, look for the ringed planet (and current "home" of Cassini)
emerging from the twilight in the constellation Gemini, about 20 degrees above the
eastern horizon. By month's end it will be almost fifty degrees above the horizon
at sunset. Jupiter rises earlier as the month progresses, almost 5 hours after sunset
as we begin the month, only 3 hours after sunset by time we turn our calendars to
By the end of February, Mercury will have moved back to the evening sky. Early in
the month Mercury and Venus are low on the eastern horizon at sunrise. Their orbits
will carry them into the Sun's glare by the middle of the month, with swifter Mercury
visible about 15 degrees above the setting Sun on the 28th.
Three hours after sunset at mid-month, the view directly overhead will be bracketed
by Castor, Pollux, and Saturn to the southeast and Capella to the northwest in Auriga.
At this time the Milky Way will divide the sky, roughly northeast to southwest.
To the east you'll see bright Regulus in the constellation Leo. Approximately midway
between Leo and Gemini lies the open star cluster known as the Beehive; it is also
known as Praesepe, which means "the manger." Binoculars or a small telescope
will reveal several hundred stars, spanning about 10 light years. This cluster is
about 580 light years distant, and our models of stellar evolution tell us that
these stars are some 400 million years old ... much younger than our own Sun and
Orion is obvious to the south, trailed by the brightest star visible in the night
sky, brilliant Sirius in Canis Major. This bright blue star has a small "white
dwarf" companion, not visible without a large telescope. This is the burned
out remnant of a star once much like our Sun. Sirius will eventually evolve into
a red giant, like Betelgeuse (visible in Orion). When this happens, hydrogen from
its outer atmosphere may accrete onto the white dwarf, eventually erupting into
a "nova" as the hydrogen reaches critical temperature and density and
triggers thermonuclear fusion into helium.
Turning to the north, we see the familiar inverted "big dipper" of Ursa
Major above and to the right of Polaris. Cassiopeia is to the northwest, its familiar
W shape tipped sideways to resemble a Greek sigma.
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.