SKYLIGHTS
Astronomy news for the week starting Friday, October 6, 2000.
It takes the Moon 29.5 days to run through its phases, the period
the basis for our calendar month (which we stretch out to fit the
year). Since a quarter of the lunar phase cycle is slightly longer
than a week, we can have a full week with no lunar quarterings
(new, first quarter, full, last quarter). Skylight's current week
starts a day after first quarter and concludes the day before full.
The entire week is therefore spent in the waxing gibbous phase, in
which the sunrise line on the Moon slowly creeps across the visible
lunar surface. (With a telescope you can see the mountains, really
crater rims, at the sunrise line catching the first rays of
sunlight). We also begin the week, on Friday the 6th, with the
Moon at apogee, its most-distant point from Earth. As it moves
against the constellations of the Zodiac, the Moon passes south of
Neptune around midnight (in North America) the night of Friday the
6th, and south of Uranus about the same time the following night,
both planets in Capricornus.
The week belongs not so much to the Moon, however, but to the
planets. Venus, by far the brightest of all planets, is now
becoming remarkably prominent to the west in evening twilight. If
you are lucky, you might also spot Mercury down and to the right of
Venus. The little planet comes into greatest eastern elongation
relative to the Sun this week (when it is angularly farthest from
the Sun), giving it the best evening visibility for this particular
orbit. However, the planet remains elusive, as the western evening
portion of the ecliptic (the apparent path of the Sun, which the
planets closely follow) lies close to the horizon this time of
year, and as a result, Mercury stays in bright twilight.
Later in the evening, Saturn, and brighter Jupiter, make their
marks in the east, both well above the horizon by 10 PM. The pair
are now wonderful showpieces in the early morning sky at dawn, both
nearly overhead and set within the jewel-like stars of Taurus, the
yellowish colors of the giant planets beautifully contrasting with
Taurus's bright star Aldebaran. To the south at that time are the
great icons of winter, Orion, with reddish Betelgeuse and blue-
white Rigel, and down and to the left, the brightest star of the
sky, Sirius in Canis Major. Early morning is a fine time to view
such stars as the weather is still warm and many of the lights of
town have been turned off, allowing the sky to be dark once
again.
The evening is not without its charms, however, as by 10 PM the
Great Square of Pegasus is high to the southeast, and the "W" of
Cassiopeia is climbing the northeast. Look too to the lonely star
Fomalhaut in Piscis Austrinus, the Southern Fish, as for most
people in North America it glides above the southern horizon.
