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Lenticular clouds

Photo of the Week. Lens like "lenticular" clouds formed by upwelling waves add a lovely softness to the blue sky.

Astronomy news for the week starting Friday, November 24, 2006.

The Moon begins the week in its waxing crescent phase as it heads toward first quarter the night of Monday, November 27th, the exact phase reached about the time of Moonset in North America, after which it waxes in the gibbous phase. Though one is hardly aware of it, the Moon will pass south of Neptune on Sunday the 26th and then two days later south of Uranus.

For awhile now, all the ancient bright planets but Saturn have been hovering near the Sun. This week Mercury breaks out of the pack, reaching a greatest western elongation of 20 degrees to the west of the Sun on Saturday the 25th. Though the angle is far from the possible maximum, the tilt of the ecliptic relative to the horizon is such that the planet rises rather well up in morning twilight fairly far down and to the left of Spica in Virgo. This appearance is rather unusual, in that Mercury actually rises slightly BEFORE the beginning of formal dawn. Jupiter and Mars remain lost in morning twilight, while Venus has yet to clear evening's last glow. They will begin to break out toward the end of the year.

That again leaves the sky to Saturn. Rising around 10:30 PM, the planet more and more becomes an evening object. Look for it just to the east of Regulus in Leo, the planet 2.4 times (nearly a full magnitude) the brighter of the two. Even a small telescope will reveal not just the rings, but a small "star" near the planet that is Saturn's largest satellite, Titan, the only satellite in the Solar System with a thick atmosphere, one whose clouds are believed to rain liquid methane.

From mid north America, Cassiopeia rides high in early evening, while the Big Dipper circles low under the North Celestial Pole, which is marked nicely by modestly bright (second magnitude) Polaris (the Little Dipper dipping beneath the pole as well). From the Earth's mid-southern hemisphere, the Big Dipper's disappearing counterpart is the Southern Cross, while high up, the two Magellanic Clouds -- satellite galaxies of ours some 170,000 light years away -- make a nice appearance, all going around the South Celestial Pole held by dim Octans, the Octant.
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