Astronomy news for the week starting Friday, October 9, 1998.
The Moon runs through its third quarter this week, passing the
phase on Monday the 12th just about the time of sunrise as the Moon
is crossing the celestial meridian to the south. With the Sun not
far to the east of the autumnal equinox in Virgo, the third
quarter, which is 90 degrees to the west of the Sun, will appear
close to the summer solstice in Gemini, the constellation's bright
stars making a nice setting to the west of the Moon. During the
rest of the week, the Moon descends in early morning hours toward
the eastern horizon as a waning crescent. On the morning of
Thursday the 15th, the crescent will be to the west of Mars and
close to the bright star Regulus in Leo, the next morning to the
east of the red planet.
Early risers can see Mars zipping quickly to the east against the
stars of central Leo as it continues ahead of us on its orbital
path. Mars's reddish color is caused by iron oxide in the dust
that covers much of the planet. The dust is so fine it can get
kicked up by wind storms in the thin atmosphere and for a time can
hide surface details from view. No rain is associated with the
storms as the planet is very dry, only a tiny amount of water vapor
in the atmosphere.
Those who do not rise early can admire brilliant Jupiter climbing
the southeastern sky after sundown. There we find no dust at all,
the telescope showing nothing but perpetual banks of clouds laid
out in a striped pattern and made largely of ammonia crystals. It
and the next planet to rise, Saturn, which is not far to the east
of Jupiter, are thought to be made mostly of liquid hydrogen buried
far below their deep gaseous atmospheres.
As we move deeper into autumn, look for the W-shape figure of
Cassiopeia climbing the northeastern sky, circling the pole
opposite the Big Dipper. To the east, find the Pleiades star
cluster -- the famed Seven Sisters of Greek mythology, daughters of
Atlas -- rising above the Vee-shaped head of Taurus, made by the
stars of the Hyades cluster. The Pleiades auger the coming of
Orion and the constellations of winter. They are famed in all
cultures. For the Inca of Peru they were a harvest basket, to the
Polynesians "little eyes," to the Navaho, who called them
"Dilyehe," they were dancers or warriors. To these and others they
were -- and still are -- a celestial timepiece that tell the
passing of the hours and the seasons.