SKYLIGHTS
Astronomy news for the week starting Friday, October 16, 1998.
The Moon wanes during the early part of the week toward new, which
it passes on Tuesday, the 20th. Sunday morning (the 17th) before
dawn, the Moon will be well down and a bit to the left of bright
reddish Mars, near the Leo-Virgo border. Two weeks ago, the full
Moon coincided with perigee, when the Moon was closest to the Earth
on its elliptical path. New Moon now more or less coincides with
apogee, when the Moon is over 11 percent farther away, reducing the
effects of the so-called "spring tides," which take place when the
Moon and the Sun are aligned. By the night of Wednesday the 21st,
a very thin crescent will be visible in evening twilight, the
growing or waxing crescent much more visible the following
night.
All the talk of the potential Leonid meteor shower in November
obscures one of the better showers of the year, which takes place
during all of this week, peaking on the morning of Wednesday
October 21. The reliable Orionid meteor shower typically produces
about 20 meteors per minute, radiating generally out of the
northern part of the constellation Orion. No or little moonlight
will make the fainter meteors easy to see, at least if you are in
a dark site. The best time is shortly before dawn when Orion is
high in the sky to the south. Meteor showers are seen when the
Earth passes through or near the orbit of a disintegrating comet
that is flaking off bits of dust and rock as their binding ices
melt away under sunlight. The stuff hits the Earth's atmosphere at
speeds of tens of kilometers per second, heats the air, and we see
a streak across the sky, the pieces themselves never reaching the
ground. What makes the Orionid shower particularly special is that
it is related to famed Halley's Comet, which has a 76-year
elliptical orbit around the Sun and last came past us in 1985. In
about six months the Earth passes near the comet's orbit again,
resulting in the "Eta Aquarid" shower of early May. Watch for a
"falling star" in the early morning hours this week to see Halley's
continuing legacy.
If you prefer to watch the sky in the early evening, be sure to
admire brilliant Jupiter to the southeast, the planet now moving
retrograde, or westerly, through the stars of eastern Aquarius just
west of Pisces. These two constellations of the zodiac are dim and
hard to find, but both contain small rather prominent "asterisms"
that Jupiter can help locate. Look up and to the right of the
planet to find a small triangle of stars with another in the
triangle's center, the figure representing "Water Jar" of Aquarius.
Then look almost directly above Jupiter to locate the "Circlet" of
Pisces, representing the head of one of the celestial fishes.
