SKYLIGHTS
Astronomy news for the week starting Friday, October 22, 1999.
All sorts of things happen at about the same time this week. The
Moon passes its full phase on Sunday the 24th in the middle of the
afternoon in North America, therefore rising just past full and
just after sunset among the faint stars of southern Aries. The day
before, on Saturday the 23rd, Jupiter comes into opposition with
the Sun, rising at sunset, setting at sunrise, and crossing the
celestial meridian to the south at local midnight (1 AM daylight
time). Since the full Moon is also opposite the Sun, Jupiter and
the full Moon will rise close together the night of Sunday the
24th, Jupiter a bit in advance and to the northwest of our
satellite. Saturn, only 15 degrees to the east of Jupiter, rises
about an hour later. Since the Moon moves about 13 degrees per day
against the stellar background, it will rise to the southeast of
Saturn the night of Monday the 25th. Later in the week, the night
of Tuesday the 26th, the Moon will pass to the north of Aldebaran
in Taurus.
Not only is Jupiter in opposition to the Sun, but little Mercury
reaches greatest eastern elongation, when it is as far to the east
of the Sun as it can get, also on Sunday the 24th. Unfortunately,
the evening ecliptic, to which the planets cling, lies quite flat
to the horizon, and Mercury is rather lost in western twilight
glare. The day before, on Saturday the 23rd, Uranus, just to the
east of Neptune, ceases its westerly motion against the stars of
Capricornus, and begins once again its normal easterly movement as
it slowly orbits the Sun.
Attention drawn to the rising full Moon makes observers note the
apparent huge size of the lunar disk. The Moon in fact is no
larger when on the horizon than it is when high in the sky (one-
half a degree). Its apparent large size is only an optical (and
well-studied) illusion. In fact the Moon is a bit angularly larger
than usual this week, as it passes perigee, its closest point to
the Earth, on Tuesday, the 26th, but that effect is actually not
sensible to the human eye.
Finally, the week is also host to one of the year's better meteor
showers, the Orionids, which peak on Thursday, the 21st, the
meteors best seen in the early morning hours after the rising of
Orion. Unfortunately, the bright waning gibbous Moon will blot out
the fainter ones. Nevertheless, a few bright meteors, the debris
of Halley's Comet, may still be observed competing with the
brilliant morning glow of Venus, seen to the east before dawn.
