SKYLIGHTS
Astronomy news for the week starting Friday, September 29,
2000.
As autumn deepens and the northern hemisphere chills, the slim
crescent Moon appears in western evening twilight, heading toward
first quarter, the phase reached on Thursday, October 5, just about
the time of sunrise in North America. By evening, the Moon
(positioned low in the south in Sagittarius) will be just past the
formal quarter. With the Sun having recently passed the autumnal
equinox, this first quarter will be the lowest of the year (and the
highest for the equivalent mid-latitudes in the southern
hemisphere). A day after the quarter, the Moon also passes apogee,
when it is about 5 percent farther from the Earth than average.
The combination will produce especially weak tides at the coasts.
The evening of Friday, September 29, we will witness a fine
conjunction between Venus and the Moon, the bright planet down and
to the left of the lunar disk, whose dark side will be well-
illuminated by earthlight. Find a clear western horizon during
twilight to view this classic sight. If your horizon is especially
clear, look several degrees down and to the right of Venus to find
Mercury. Oddly, only a few hours later, the Moon will pass the
asteroid Ceres, and actually cross over it, although after moonset
in continental North America (the event visible from Hawaii).
Saturn entered its retrograde motion on September 12. To the west
of Jupiter (and rising around 9 PM), Saturn began pulling away from
the giant planet. Now it is Jupiter's turn, as it stops its normal
easterly motion on Friday, the 29th, and also begins to move
retrograde, or westerly, against the stellar background of Taurus.
Closer to us than Saturn, Jupiter's apparent movement is faster
than that of the ringed planet, and the two will soon begin to draw
somewhat closer, though Jupiter is too far to the east of Saturn to
overtake it.
As October begins, Cepheus is at its northern-hemisphere early-
evening highest, though a fairly dark sky is needed to see most of
the stars of the dim, large distorted pentagon that makes the
celestial King, Andromeda's father. At the same time, much
brighter and better-known Cassiopeia, the Queen, is climbing the
northeastern sky. Cygnus, now overhead in mid-evening for most
northerners, stands upon a stack of constellations that leads to
the south through Delphinus, the Dolphin, and into western Aquarius
and Capricornus. If you are south of 30 degrees north latitude,
the bright second magnitude star with the modern name "Peacock" in
Pavo, the celestial peacock, makes an appearance. Capricornus, the
"water goat," to the west of the quarter Moon, marks the beginning
of a string of three watery constellations, itself, Aquarius (the
water bearer), and Pisces (the fishes). Called the "wet quarter,"
the trio contain the memory of a long-past rainy season.
