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Thin Moon

Photo of the Week. A thin waning crescent sets in mid-August summer twilight.

Astronomy news for the week starting Friday, October 19, 2007.

The Moon spends the week going from first quarter, passed the morning of Friday, October 19, to full, which hits around midnight (for North America) the night of Thursday the 25th near the Pisces-Aries border. Just seven hours after the formal full phase, our companion also passes perigee, where it is just over five percent closer to the Earth than average (resulting in especially high tides at the coasts). This full Moon will thus be near its largest possible angular diameter, although the effect is not visible to the eye. (That a full Moon seems to rise large, looming on the horizon, is but an optical illusion that has nothing to do with special angular size.)

As the Moon travels, it splits the difference between Neptune and Uranus rather like a game of celestial croquet, passing south of Neptune (in northeastern Capricornus) the night of Saturday the 20th, then north of Uranus (in northeastern Aquarius) almost exactly two days later. (Neptune is actually occulted as seen from parts of Antarctica.)

Slowly moving to the west of Venus, Saturn rises around 3 AM Daylight Time, about half an hour before its much brighter morning companion, which lofts itself up over the eastern horizon around 3:30 AM. Look early in the week to see the two planets making a trio with Regulus in Leo, the star on top, Saturn down and to the left, Venus almost equidistantly below Saturn.

As Venus is to the morning sky, Jupiter is to the evening, although given its southwesterly position, the giant planet is a bit less obvious. Now setting just before 9 PM Daylight, Jupiter still lingers in a dark sky for an hour past the end of evening twilight (twilight actually being the best time to see the giant planet). Still in deep southern Ophiuchus to the northeast of Scorpius's Antares, Jupiter is now heading slowly toward its southern depths in Sagittarius. One planet you won't see is Mercury, which passes inferior conjunction with the Sun on Tuesday the 23rd.

Try to catch some Orionid meteors the mornings of October 21 to 23, when they can hit 25-30 meteors per hour.

While Sagittarius is among the more prominent of the zodiacal constellations, boasting two bright asterisms (the "Little Milk Dipper" and the "Teapot"), its neighbor to the east, Capricornus, is among the dimmest, vying with Cancer as one of the more obscure patterns, and hard to see. Yet it is not without its charms. It is the first constellation of the "wet quarter" that also includes Aquarius, Pisces, and a couple others, holds a pretty line-of-sight double (Algedi), and a beautiful globular cluster, Messier 30.
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