March 2004 Sky from the Keeble Observatory
The Mars rovers, Spirit and Opportunity, are performing beautifully. Spirit landed
first, at a site known as Gusev Crater. This site gave some evidence from orbiting
probes that the crater once held a lake. The crater floor is also relatively smooth,
so it made a "safe" yet scientifically important site. Early computer problems,
which nearly disabled the rover because the "flash memory" was overloaded with 7
months' data from the trip to Mars, have been overcome. The daily routine includes
repositioning the rover to examine rocks and soil with its array of instruments,
including a grinding tool to drill into some of the rocks. Over then next several
weeks, the rover will travel towards a small crater about a kilometer from its landing
Opportunity landed at Meridiani Planitia (Meridian Plane), also smooth and safe.
The Meridiani site was selected because orbiting instruments detected the presence
of the iron-oxide bearing mineral hematite which, on Earth, forms in the presence
Controllers were ecstatic about a "hole in one" … Opportunity bounced to a stop
in a shallow crater where it could examine exposed bedrock. Some of the rock appears
to be layered … it's either sedimentary, or has been laid down in thin layers of
volcanic ash and windblown dust. The hematite content of the region has been confirmed
by infrared spectroscopy; the question remains open whether it formed in water,
or whether some mechanism involving ultraviolet light from the Sun formed it from
iron-rich rock reacting with water vapor in the atmosphere.
The overall mission of both rovers is to seek confirming evidence that water was
once relatively abundant on the surface of Mars. We think so; running or ponding
water could explain many of the surface features observed from orbit. But, the scientific
process demands more than "it looks like it might have been done by water." Rather,
we need direct evidence. Finding ice would be nice, but is not likely so far from
the polar caps. Finding chemical evidence that the minerals formed in water rather
than in a dry climate is needed.
We'll say much more about these probes as they get further into their primary 90-day
Lunar phases for March: Full Moon (on the opposite side of the sky from the Sun,
so that it rises at sunset and sets at dawn) on the 6th; Last Quarter (90 degrees
east of the Sun, so that it rises at noon and sits due south at sunset) on the 13th;
New Moon (in the same general direction as the Sun, so that it rises and sets at
the same time as the Sun) on the 20th - also the Vernal Equinox at 1:50 am; First
Quarter (90 degrees west of the Sun, due south at sunrise, setting about noon) on
March is an excellent month for evening planet watchers! As the sky emerges in the
evening twilight, Venus will be the brightest object to the west. It's high in the
sky so you can watch it for several hours until it disappears into the horizon clutter
and haze. Mars is almost directly above Venus. It will appear a pale orange in contrast
to the brilliant Venus, but it will show a small round disk in a telescope, contrasted
with Venus' larger "first quarter" phase. Venus is catching up to us in its orbit,
so look for it to begin moving closer to the Sun on the sky as the month continues.
Saturn is almost directly overhead at sunset, its rings will be spectacular in a
small telescope. Jupiter is near opposition early in the month; look for it to rise
around sunset, and be visible virtually all night.
An overhead view about two hours after sunset finds the constellation Gemini overhead.
The bright "twins" of Castor and Pollux are just to the south of zenith. Saturn
is an interloper in the constellation, to the west of Pollux. Towards the east we
see the constellation Leo, with its brightest star Regulus marking the heart of
the Lion. Jupiter lies just below Regulus. To the west of Saturn, your eyes will
pick out the well-known asterism of the Pleiades, and just below them the planet
Mars. That bright star near the Pleiades is Aldebaran, in the constellation Taurus.
Orion starts the evening above the southern horizon, with the familiar three stars
of the belt its most famous feature.
Of some excitement to astronomers has been the recent discovery of a "new" reflection
nebula above the belt, near an older complex known as M78. Known as McNeil's Nebula,
this feature wasn't there as recently as last fall! It marks the emergence of a
newly formed star or cluster from the near edge of the Orion Molecular Cloud, nearly
1500 light years distant. You won't be able to see this without very clear skies
and a more than modest telescope.
Ursa Major (more commonly the "Big Dipper") is to the northeast, and will circle
above Polaris as the night advances. When it gets high enough, test your eyes on
the middle of the "handle." How many stars do you see there? Mizar and Alcor are
a binary which many but not all folks can see as separated without a telescope.
In a telescope, we would see that both stars actually look like binaries themselves.
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.