Photo of the Week. A five-day old waxing crescent
descends the blue sky.
Astronomy news for the week starting Friday, September 16,
2011.
The Moon
begins our week in its waning
gibbous phase in which we see mostly daylight on the lunar disk
with the nighttime side there, but unseen, as a dark crescent.
Gibbous finally gives way to third
quarter on Tuesday, September 20, in the morning before Moonset
in North America, allowing you to see a fine third quarter in
daylight hours. Passing from the stars of eastern Taurus, we then get to catch a few
days of the waning crescent. The lunar
week features planetary bookends. The night of Friday the 16th,
the gibbous Moon will be set to the northeast of Jupiter, while
on the morning of Friday the 23rd, the crescent will glide five
degrees south of Mars, with great
Leo seen rising to the east of the
pair as dawn approaches.
Obviously, our current planetary jewels are Jupiter and Mars.
Jupiter, slowly retrograding westward in southern Aries, is now rising brilliantly to the north of east
around 9 PM Daylight Time, less than half an hour past the end of
twilight. Follow it across the sky to 3:30 AM, when it crosses the
meridian to the south and enters the
western celestial hemisphere. By then, Mars, rising in the
northeast about 2 AM, is well up, the two planets beautifully
punctuating the heavens. Leaving bright Gemini to the west, Mars, moving to the east against
the stars, passes into dim Cancer
as our week begins.
The big event, however, involves ourselves, as on the morning
Friday the 23rd, at 4:05 AM CDT (5:05 EDT, 3:05 MDT, 2:05 PDT), the
Sun passes
the autumnal equinox in Virgo, which marks the beginning of
fall in the northern hemisphere (spring in the southern). By the
time we are graced with daylight, autumn will already be in
progress, summer behind us. On that day, the Sun will rise very
close to due east, will set due west, be up for 12 hours (actually
a bit more because of the solar diameter and refraction in the
Earth's atmosphere), and be down for 12. The day also marks the
more or less formal setting of the Sun at the north
pole and its rising at the south pole (though
for reasons given above, the Sun is already up at the south polar
station).
With the Moon gone from the evening sky, if you are in a dark
location, you might once again admire the Milky Way, made of the combined light of
the billions of stars in the disk of our Galaxy. Highly irregular,
the Milky Stream is given great character by the Galaxy's dark,
star-birthing dust clouds. From Cygnus, overhead in mid-evening, the path is split in
two by the Great Rift, the brighter eastern side passing to the
south through Aquila, Scutum (where it gathers into a fine
star cloud), and into Sagittarius.
