Keeble Observatory
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 point.
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 of water.
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 missions. To follow their missions more closely,
point your browser to http://mars.jpl.nasa.gov/mer
.
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 the 28th.
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.
You can see an image at http://antwrp.gsfc.nasa.gov/apod/ap040219.html
and several links from that web site at NASA's Goddard Space Flight
Center.
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.
Copyright 2004
George Spagna