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

Cloud Shadows

Photo of the Week. Clouds throw their shadows toward the ground below.

Astronomy news for the week starting Friday, October 28, 2005.

We begin the week with the Moon in its waning crescent phase, each morning becoming closer to the horizon and more into dawn. Always with us, it will then just SEEM to disappear for awhile as it goes through its new phase, passing more or less between us and the Sun (missing it, so no eclipse) on Tuesday, November 1. It will thereafter become visible as a slim waxing crescent in bright western twilight the night of Thursday the 3rd. Watch as the growing crescent moves out of the evening's glow and also partners both the inner planets, Mercury and Venus.

In a very unusual coincidence, these two planets reach their greatest eastern elongations almost simultaneously, within three hours of each other, on Thursday November 3. (At greatest eastern elongation, they are farthest in angle to the east of the Sun and therefore near best visibility at night; at greatest western elongation, they are best visible in the morning.) On that date, Venus will be 47 degrees to the east of the Sun, while Mercury will be 24 degrees to the east. The low angle of the evening ecliptic to the horizon, however, makes the planets rather hug the ground. While Venus is eminently visible in the early evening (the brightest thing in the sky other than the Moon), Mercury's visibility is severely compromised by low altitude for those of us in the northern hemisphere. Because the evening ecliptic will be coming back upward, Venus will oddly seem to climb in the sky farther out of twilight in spite of getting closer in angle to the Sun, setting later and later until late November. It will also keep getting brighter until December 9, when it peaks. Now add the Moon. The night of Thursday, November 3, the thin crescent will lie just below Mercury, making it possible to find the little planet -- use binoculars. Two nights later, on Saturday the 5th, the waxing crescent will lie just to the left of Venus in a near-classic pairing.

As the sky darkens, you can then look to the east to see very bright Mars (now in southeastern Aries to the north of the head of Cetus). Continuing the planetary coincidences, Mars is closest to Earth in its current round of visibility (70 million kilometers, 43 million miles), and therefore brightest, on Saturday October 29th. It will pass opposition to the Sun, when it rises at sunset and sets at sunrise, on Monday, November 7. (The two dates do not coincide because of the eccentricity of the Martian orbit.) Later in the evening, watch for the rising of Saturn at midnight daylight time, the ringed planet ensconced in Cancer just southeast of the Beehive Cluster.

The stars of the Andromeda myth are now on wonderful display in mid-evening, the gang of six constellations led to the west by rather dim Cepheus, the King, whose Queen, famed W-shaped Cassiopeia, is seen rising high in the northeast. Cepheus himself forms a much fainter pentagon whose best-known resident Delta Cephei, the prototype of the Cepheid variables that provide us with a measuring stick with which to establish the distance scale of the Universe.
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