Keeble Observatory
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 Galaxy.
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
20th.
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.
Copyright 2006
George Spagna