SKYLIGHTS
Astronomy news for the week starting Friday, November 10, 2000.
We begin the week with the near-full Moon, the phase passed on the
afternoon of Saturday, November 11, shortly before moonrise in
North America when it is moving between Aries and Taurus. That
same night, the now-waning Moon will be seen up and to the right of
Saturn, the Moon, Saturn and Jupiter lying on a curved line. The
next night, that of Sunday the 12th, the Moon will fall between the
two planets, and make a fine tight triangle with Jupiter and
Taurus's Aldebaran. The brilliance of Jupiter (which the bright
Moon cannot overcome) and the apparent closeness of the two will
make the lunar motion easily visible, the Moon moving its own
diameter in about an hour. Continuing the succession of days, on
Tuesday the 14th, the Moon will pass perigee, when it is closest to
the Earth.
The planetary list this week is topped by Mercury, as it will be at
its greatest western elongation, that is, when it is as far west of
the Sun as possible, the morning of Wednesday, the 15th. If you
have never seen the little planet, this week gives a fine chance,
one of the best of the year. Look to the southeast in growing
twilight for a bright starlike point near the horizon. While quite
bright, the planet is notoriously hard to see because of its
proximity to the Sun, which makes it visible to the naked eye only
in twilight and through the murk of the thick air near the horizon.
Through the telescope, Mercury now takes on the appearance of a
quarter-moon, as we see one-half in daylight, the other half in
night. The poor visibility of Mercury makes it extremely difficult
to see features on the planet, and most of what we know comes from
radar studies and from the 1974-75 flybys of the Mariner 10
spacecraft, which showed the planet's ancient surface to be
devastated by heavy cratering much like that of the Moon. Though
the smallest planet (excepting odd Pluto), it has the distinction
of being the densest and having the largest iron core relative to
its size of any of the nine. And while admiring the association of
the Moon with the giant planets and contemplating Mercury, do not
forget brilliant Venus, easily seen now in the southwest after
sundown.
The northern hemisphere is now in Cassiopeia season. From mid-
northern latitudes, the famed "W" is nearly overhead around 9 PM.
Opposite Polaris and the North Celestial Pole, the Big Dipper
glides along the northern horizon. From above 41 degrees north
latitude, the Dipper is circumpolar, never setting at all. If you
have a clear northern horizon, take a look. The well-known "Moon
illusion" artificially makes the rising full Moon look huge when on
the horizon. Constellations suffer the same effect, the Dipper
looking enormous as its parent constellation, Ursa Major, the Great
Bear, walks beneath the pole.
