Skylights featured on Astronomy Picture of the Day

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Skylights featured five times on Earth Science Picture of the Day:
1 , 2 , 3 , 4 , 5

Waning crescent

Photo of the Week. A very thin waning crescent Moon reveals its nighttime side eerily awash with light from a nearly full Earth. The irregularities in the bright lunar daytime edges are real, and are caused by crater rims catching the last rays of sunlight. The dark areas, which in full Moonlight make the "man in the Moon," are giant impact basins. The large ghostly crater at far right is Tycho. Photo by Mark Killion.

Astronomy news for the week starting Friday, December 23, 2005.

Welcome to the last full week of the year, with wishes to everyone for a good holiday season. The week begins on Friday, December 23rd, with the third quarter Moon and proceeds with the Moon running through its waning crescent phase almost to new, which it will pass next Friday, the 30th.

As the Moon goes along to the east against the stellar background, it makes a bunch of passages. On Christmas morning before dawn, the Moon will be seen approaching Spica in Virgo, and actually occulting it for those in western North America (where it is dark, around 6 AM PST). The Moon next takes on Jupiter, passing a few degrees to the south of the giant planet shortly before it rises on the morning of Tuesday the 27th. The next morning watch for it just below bright Dschubba, Delta Scorpii, and up and to the right of Antares, which it will occult for as seen from the eastern hemisphere. Finally, the morning of Thursday the 29th, the Moon will rise just before dawn as a very slim and pretty crescent (see the above photo). As it proceeds, watch for Earthlight to grow on the nighttime side.

As the year approaches its end, Venus is quickly slipping away. At week's end, it sets just as twilight fades. Its place is taken by Saturn and Sirius, which rise just a bit later, about 7:30 PM, half an hour before bright reddish Mars (still in Aries) crosses the meridian to the south. Wait then until 3 AM when Saturn takes its turn at the meridian, half an hour after which Mars sets and Jupiter rises, all in a lovely symmetric dance.

In early evening look high, close to overhead, for streams of stars that make the maiden Andromeda, who is perpetually poised to be rescued by Perseus to her east. The westernmost star of the constellation, Alpheratz (Alpha Andromedae) serves also as the northeastern corner of the Great Square of Pegasus, the famed asterism of Pegasus, the flying horse on which Perseus forever rides. South of the southern curve of Andromeda, look for two stellar triangles, the northern one Triangulum (the eponymous Triangle), the southern the main figure that makes Aries, the Ram, the constellation of the Zodiac that held the Vernal Equinox in ancient times (because of precession, the 26,000 year wobble of the Earth's axis, that job now taken over by Pisces).
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