Photo of the Week. Wind-blown clouds adrift in a blue
sea.
Astronomy news for the week starting Friday, September 3, 2010.
The Moon goes through its new phase this week on Wednesday,
September 8, its absence from the nighttime sky allowing us a fine
view of the stars. During most of the week we see the Moon fade
away in its waning crescent, with the
last reasonable view in eastern morning twilight being on Monday
the 6th. We then do not pick it up again until the evening of
Thursday the 9th as an ultra-thin waxing
crescent in western evening twilight. That same day, the
crescent passes several degrees south of Saturn, the
event effectively invisible. Better to wait until the following
evening to spot our lunar companion. Six hours before new, the
Moon passes perigee, where
it is closest to the Earth, pairing of the two bringing especially
high and low tides
to the coasts.
The evening planetary sky is but a ghost of what it has been.
Saturn is now lost to evening twilight and Mars, while
still more or less visible, has much faded as it passes two degrees
north of Spica in Virgo on Saturday the 4th, the first
magnitude star 60 percent brighter than the planet, which has
slipped to bright second magnitude. Venus, however,
remains in charge of evening twilight (Mars up and to the right of
it). Low in the sky, the planet continues to brighten some as it
approaches Earth. After reaching maximum brilliance in late
September, it will rapidly exit the evening, only to pop up in
November's morning sky. A telescope shows a crescent, as
the daytime side is obviously facing the Sun,
with mostly nighttime then facing Earth.
As Venus sets at the end of twilight (around 9 PM Daylight Time),
Jupiter then
rises in the east. Pulling an all-nighter, it transits the meridian to the south about 2 AM. Look
for it to the southwest in morning twilight, which is rapidly
getting later and later as the Sun moves to the south along its ecliptic path.
If you are lucky enough to find a dark location, with the Moon out
of the way, this is a fine time to admire the Milky Way as it cascades from the north
through Cygnus and Deneb down through Aquila and Altair. It brightens to the south
through modern Scutum and then hits
its peak in Sagittarius, where it
is sadly dimmed for northerners by the Earth's thickening
atmosphere. To the east of Cygnus, we see the rising of that
harbinger of Fall, the Great
Square of Pegasus, as Cassiopeia climbs the northeastern
sky.
