SKYLIGHTS

Astronomy news for the week starting Friday, October 13, 2000.

We begin our week with the full Moon. The nearly-full-Moon having risen the night of Thursday, the 12th, the phase is reached early this morning, the Moon rising just past full the night of Friday the 13th within the confines of the dim constellation Pisces. As the phase fades toward third quarter, reached the night of Thursday the 19th (only a day after it also passes perigee, when it is closest to the Earth), the Moon will provide excellent punctuation for both Saturn and Jupiter as it passes against the bright stars of Taurus. The night of Monday the 15th, the lunar disk will appear less than two degrees south of the ringed planet, while the following night it will appear below Jupiter, when the planet, the Moon, and orange Aldebaran will make a tight triangle.

The passage makes a fine opportunity to note the tilt of the lunar orbit. Jupiter in particular is now very close to the ecliptic, the apparent path of the Sun, while the Moon will be notably to the south of it. The Moon's path is tilted by 5 degrees to the ecliptic, which is why we do not get eclipses of the Sun and Moon each month, as the Moon usually passes above or below the Earth's shadow at full Moon or above or below the Sun at new. Only twice a year, when the Moon is actually on and crossing the ecliptic during either full or new, are conditions right to have eclipses.

Since last May, Uranus and Neptune, both in Capricornus, have been in retrograde (as are now both Jupiter and Saturn, the quartet all moving west against the stellar background). Neptune, the most distant, dimmest, and currently westerly of the four, is the first to cease its retrograde motion, and on Sunday the 15th once again resumes normal easterly movement. Uranus will follow shortly. Be sure also to note Venus, now increasingly brilliant in the southwest. Because the evening ecliptic this time of year lies relatively flat against the horizon, the planet is still not terribly far above the horizon, a situation that will correct itself as the winter approaches.

While the Moon's phase and brightness diminish, the Orionid meteor shower climbs in prominence. While not reaching its peak until the night of Saturday, the 21st, it lasts over 10 days, and its meteors -- the debris of Halley's Comet -- can be seen flashing through the sky in the early morning hours well before the maximum. The Earth passes near Halley's orbit twice, the other time in early May, when Halley's leavings create the Eta Aquarid shower.

Finally, keep your eye on the autumn constellations as they climb the evening eastern sky, all those of the Perseus myth -- Cassiopeia, Cepheus, Andromeda, Pegasus, Cetus, and Perseus himself -- there to admire.