Astronomy news for the week starting Friday, September 5, 2008.
The Moon begins our busy week as a fat waxing crescent as it heads towards first quarter on Sunday, September 7. It
thereafter grows and brightens in the waxing
gibbous towards full, which it will
not reach until next week. The early part of this week sees it
moving gloriously against the background of the two deep southern
constellations of the Zodiac, Scorpius and Sagittarius. The night of Friday the 5th finds the
Moon to the west of the Scorpion's three-star head. The next
evening (Saturday the 6th), the Moon comes into close conjunction
with (just to the south of) bright reddish Antares. Two nights later, on
Monday the 8th, the Moon will be shifted northwest of the Teapot of Sagittarius, and then the
following night (Tuesday the 9th) it takes on Jupiter, which will
lie to northwest of the Moon (the two having passed conjunction
during the day). An hour after the Moon passes first quarter, it
also passes
apogee, where it is farthest from the Earth.
The early evening twilight sky contains a remarkable, though
largely invisible, grouping of three planets,
Venus, Mercury, and
Mars, the latter the
dimmest and without optical aid quite invisible. Try, though, to
find the brightest, Venus, which climbs a bit higher each night.
On Wednesday the 10th, Mercury hits greatest eastern elongation,
though the low tilt of the ecliptic makes it hard to see
below and to the left of much brighter Venus. At nearly the same
time, Mercury and Venus come into formal conjunction four degrees
apart, while on the following two days both
of them pass conjunction with Mars.
Then, rather oddly, it's on to the greatest and smallest of
planets, Jupiter and Pluto. (Is Pluto a "planet?"
The semantic argument still rages. It is what it is, the nearest
and almost biggest within the band of debris beyond Neptune called
the "Kuiper
Belt." Perhaps from its history, we can call it an "honorary
planet.") Jupiter, just above the Little Milk Dipper of Sagittarius, ends its
retrograde motion (westerly against the stellar background) on
Sunday the 7th, and then begins its long slow climb toward Capricornus. The following day, that
of Monday the 8th, Pluto (also in Sagittarius roughly 15 degrees to
the northwest of Jupiter and near the border with Ophiuchus) does the same thing.
But while brilliant Jupiter is easily seen to the south as twilight
draws to a close (not setting until around midnight), Pluto, 1500
times fainter than the faintest star visible to the naked eye,
requires a decent telescope to see.
After admiring early evening's Scorpius and Sagittarius, lift your eyes upward to the
Summer Triangle of Vega (nearly overhead), Deneb (at the top of Cygnus's Northern Cross), and Altair (a bit south). Following
along behind Cygnus will be the Great Square of Pegasus, telling us that autumn is not far behind and
that the summer gang will soon be gone.
