March 2006 Sky from the Keeble Observatory
Astronomy is a rapidly changing field, with new information coming almost daily.
Here are three items which caught my attention in the past week:
Researcher Neil Gehrels, principal investigator for NASA’s Swift satellite, announced
detection of an unprecedented gamma ray burst. The explosion was detected on 18
February, and it was both much closer (a mere 440 million light years!) and lasted
almost 100 times as long (nearly half an hour!) as previously known bursts. These
observations have been interpreted as possible precursors to a supernova, which
now means that lots of telescope time across the electromagnetic spectrum will be
devoted to further monitoring. Normally, we don’t get a warning, so we only see
the supernova after it explodes.
Mars Reconnaissance Orbiter will arrive at Mars on the 10th. If all goes well, it
will brake into its initial elliptical orbit with a 27-minute firing of its main
rocket engine. However, we have less than a 60% success rate with putting probes
into Martian orbit – so flight controllers will be biting finger nails and dosing
heavily on antacids. Assuming a safe orbital insertion, the probe will begin a year-long
process of dipping into the thin atmosphere to brake the orbit into a lower circular
one before the instruments are activated.
A newly completed 10-year survey by the Rossi X-ray Timing Explorer satellite has
mapped the sources of the diffuse x-ray background from the Milky Way. Previous
researchers had been puzzled by this radiation, because there did not appear to
be a good explanation for its source. That has been settled with the much improved
angular and wavelength resolution of the new survey. Rather than requiring exotic
sources like black holes or supernovae, part of this background seems to come primarily
from a previously undetected population of white dwarf stars in binary systems.
White dwarfs are stellar embers, normally to faint to be seen over great distances.
In a binary system, they can accrete from the companion star hydrogen gas, which
then heats up tremendously to emit x-rays. A lower energy component seems to originate
in binary systems as well, but from enhanced x-ray flare activity, likely triggered
by tidal distortions of the stellar atmosphere. These sources suggest a substantial
under counting of these types of stars in previous estimates. Just as with a medical
x-ray, the distribution of these sources reveal clues to the structure of our home
Lunar phases for March: First Quarter on the 6th, at 3:16 pm; Full Moon at 6:35
pm, on the 14th; Last Quarter on the 22nd, at 2:10 pm; New Moon on the 29th, at
5:15 am. Note that there will be a penumbral lunar eclipse on the 14th, but don’t
expect anything spectacular – the full moon will look a little dimmer, but the central
part of Earth’s shadow (the umbra) will not intercept the lunar surface. A total
solar eclipse will be visible from parts of Africa and Turkey on the 29th – it will
all be over before the Sun rises in Virginia.
Early risers will see several planets before sunrise. At dawn, it will be difficult
to miss Venus, about 25 degrees above the southeast horizon. It’s pulling away in
its orbit, but remains very bright. It reaches its maximum westward elongation on
the 25th, when you will see it near the waning crescent Moon. Jupiter is about the
same height above the southwest horizon. It will drift westward through the month,
and will appear lower in the sky. Mercury will return to the morning sky at mid-month,
rising about an hour before the Sun by month’s end.
Speaking of sunrise, the point on the horizon where you first see the morning Sun
is drifting slowly northward. It begins the month to the right of due east, and
will rise almost exactly east on the 20th, marking the Vernal Equinox and the beginning
of astronomical spring. Sunset is also drifting north, and will be due west on the
At sunset you will find Saturn high to the east, about 75 degrees above the horizon,
near the Beehive Cluster in the constellation Cancer. At the beginning of the month
you’ll see Mercury to the west, setting about an hour after the Sun, but it moves
quickly closer to the Sun, and will be lost in the glare by the 10th, emerging into
the predawn sky after the 15th. Mars is high to the south.
Our mid-month look overhead, about two hours after sunset finds Castor and Pollux
the two brightest stars near zenith, just a little to the south. Mars is now west
of zenith in Taurus, where it spends the whole month. The bright star below and
to the left is Aldebaran, also known as Alpha Tauri. Above and to the right is Capella,
in the constellation Auriga. Still prominent, but now shifted to the southwest is
Orion. The bright red giant Betelgeuse marks the upper left corner of this familiar
shape, with the bright blue giant Rigel almost directly below, marking the lower
right corner. In between we see the signature three stars of the “belt,” with the
stellar nursery of the Orion Nebula hanging beneath as part of the “sword.” Saturn
lies ESE of zenith – binoculars will allow you to see both its rings, and the diffuse
Beehive Cluster nearby. Twenty degrees below Saturn lies the bright star Regulus,
in the constellation Leo, which is recognized by its familiar sickle shape. High
to the northeast, the inverted “big dipper” of Ursa Major points to the north and
Polaris, the “north star.”
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.