SKYLIGHTS
Astronomy news for the week starting Friday, August 27, 1999.
The Moon is in its waning gibbous phase this week, a time when most
of the visible lunar disk is in sunlight. Third quarter, which
begins the waning crescent portion of the lunar journey, takes
place on Thursday, September 2. At almost the same time, the Moon
passes its perigee, when it is closest to the Earth. As it makes
its journey against the stars of Pisces and Aries, it passes south
of Jupiter the night of Monday the 30th, then south of Saturn the
night the 31st.
Mars, moving rapidly now among the stars of far eastern Libra (up
and to the right of the trio of stars than make the head of
Scorpius) still dominates the early planetary evening sky, glowing
redly in the southwest. But it does not dominate long, as
brilliant Jupiter encroaches on the evening, rising in the east now
around 10 PM, followed within the hour by Saturn. Jupiter, the
planetary system's giant, 11 times the size of Earth, entered
retrograde, or westerly motion, last week, and now it is Saturn's
turn, as it stops travelling easterly and begins its backward trek
on Monday, August 30 (caused by the Earth beginning to swing
between it and the Sun). Though over the long haul Jupiter is
getting closer to Saturn, while the two planets are in retrograde
Jupiter will temporarily pull away.
As the Moon dims and clears out of the way, the night sky is again
revealed. One of the best times of the year for viewing, rivalled
only by the depth of winter, which contains Orion's family, late
August and early September feature the summer Milky Way. Hard to
see from town, in a dark sky the Milky Way brilliantly streams from
Cygnus (nearly overhead in mid-northern latitudes) toward the south
through Aquila and into Sagittarius where it broadens around the
center of the Galaxy. In 1610 Galileo announced that this broad
band of light consisted of countless stars. We now know it be the
combined light of the disk of our 200-billion-star Galaxy, in which
we live.
While admiring the night, don't forget the day. The third quarter
Moon appears high to the south at sunrise and is visible during
morning hours as it moves to the west. The Sun is also moving
quickly to the south as it approaches the Autumnal Equinox at a
rate of a third of a degree per day, resulting in rapid daily
changes in the time of sunset and sunrise.
