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Astronomy Picture of the Day

Nu Vir graze Nu Vir graze

Photos of the Week.. The Moon (its nighttime side illuminated with Earthlight) just barely misses a grazing occultation of Nu Virginis on July 14, 2002, the star seen just to the left of the upper horn of the bright crescent. The pictures, taken 5 minutes apart, clearly show the easterly lunar motion. The irregular outline of the bright crescent (the sunrise line on the Moon) is caused by high areas catching the first rays of sunlight contrasted with low basins still in shadow. (The glow to the right of the crescent is a photographic effects caused by the Moon's brilliance).

Astronomy news for the short week starting Friday, December 13, 2002.

The Moon, having just passed its third quarter, waxes in its gibbous phase as it heads toward full on Thursday, the 19th, around noon in North America. As a result, the not- quite-full Moon will rise just before sunset the night of Wednesday the 18th, and the just-past-full Moon will rise just after sunset the night of Thursday the 19th. The somewhat mysterious word "gibbous" comes from middle English meaning "humped," rather like a camel, as the two circular outlines of the Moon, the real edge (or limb) and the terminator (the day-night division) have different convex curvatures. Four hours before its full phase, the Moon passes Saturn , the planet falling a bit to the west (and somewhat south) of the Moon the night of Wednesday the 18th, and somewhat to the east of the Moon the following night.

Since the full Moon is in opposition to the Sun at about the same time it passes the ringed planet, it holds that Saturn should be near opposition too, which it is, passing that position on Tuesday the 17th. At that time, it will rise at sunset, set at sunrise, cross the meridian to the south at midnight, be in the middle of its retrograde motion, and be at its best visibility for the year. Moreover, it is about as far north as it can get. With a telescope we get a fine view of the south side of the famed rings, which are complex belts of fine ice-coated rocky debris in orbit about the planet. Moreover still, Saturn is near its perihelion point, and is about as close to the Earth as it can get, rendering it especially large and bright. A view with even a small telescope quickly shows Saturn's largest moon, Titan . Slightly larger than Mercury, Titan is the only satellite with a thick atmosphere.

When you are through with Saturn, you do not have long to wait to see brilliant Jupiter, which climbs above the eastern horizon shortly before 9 PM. Wait a few more hours now, until roughly 3:30 AM, and find much-brighter Venus lofting itself upward, the planet rising almost as early as possible for this particular apparition.

With astronomical winter nearly on us, the fall constellations are moving westward. There is still time, though, to admire the bright southern star Fomalhaut in the constellation Piscis Austrinus, the Southern Fish, the star low in the south around 6 PM for mid- northern latitudes. Immediately to the east you will find the dim and rather large modern constellation Sculptor, the "Sculptor's Studio." Its major claims to fame are its peculiar Alpha star, the Sculptor Dwarf Galaxy (which lies 300,000 light years away), and its possession of the South Galactic Pole, the direction that lies perpendicular to the plane of the Galaxy and of the Milky Way (the North Galactic Pole falling in Coma Berenices). Valid HTML 4.0!