Astronomy news for the week starting Friday, September 5,
2014.
The Moon begins our week late in its waxing
gibbous phase, rocks by full
phase on Monday the 8th (about the time of Moonrise in North
America), then the rest of the week dims through the early part
of its waning gibbous phase. While
the coincidence of perigee (when and
where the Moon is closest to Earth, the night of Monday the 7th)
is not as good as it was at the last full Moon, this "supermoon" (on
the average 12 percent larger than an apogean Moon) is almost as
good. There are no planetary passages of note, unless we count
one well north of Neptune on Monday the 8th and
another past Uranus on Wednesday the 10th. The
latter is a bit of a curiosity, as the waning gibbous Moon will
occult, or pass in front of, the planet as would be seen from the
far north (it's not worth a trip to Siberia). With the Sun approaching
the autumnal equinox in Virgo, this full Moon will be
riding the southern ecliptic
not far from the vernal equinox
in Pisces, the constellation's dim stars mostly
hidden by lunar brightness.
In the evening, though both are near setting by 10 PM Daylight
Time, Saturn and Mars are still quite visible as twilight draws to a
close. They are widening the gap between them, faster-moving Mars
only slowly falling behind the Earth as both orbit the
Sun. By the end of the week, the red planet will be roughly
halfway between Saturn and Antares in Scorpius, the star slightly the fainter but of similar
color to Mars (hence "Ant-Ares" after the Greek god of war). In
the morning sky, Jupiter and Venus
are separating as well. Though still bright, Venus is a challenge
as it rises half an hour after the break of dawn. Jupiter on the
other hand is shifting in the other direction, rising earlier, now
just after 3:30 AM within the confines of dim Cancer, the planet quite unmistakable as it climbs
above the eastern horizon.
The Moon will wash out most of the stars, only the brighter ones
shining through. In the northwest, though, the faithful Big Dipper is still seen, all but
one of its stars second magnitude. The
stellar brightness scale was invented around 130 BC by the Greek
astronomer Hipparchus of Nicea, who divided the naked eye stars
into six categories, first magnitude the brightest, sixth the
faintest. The system, though modified and set on a modern
mathematical scale, is still in use today. There are but 22 first
magnitude stars, which actually run into magnitude zero and -1
(Venus going to -5!). Each full magnitude is about 2.5 times
brighter than the next fainter one. Oddly, the brightest and
faintest of the first magnitude set, Sirius and Adhara, are in the same
constellation, Canis Major, Orion's larger hunting dog. Both
stars are coming onto the scene in late morning skies to the
southeast of the Hunter, giving us a preview of winter.
