Skylights featured on Astronomy Picture of the Day

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Skylights featured nine times on Earth Science Picture of the Day: 1 2 3 4 5 6 7 8 9


Photo of the Week. Squashed sunrise, the Sun distorted by atmosphric refraction, which raises the lower edge farther up than the upper. As the Sun climbs, the effect rapidly disappears.

Astronomy news for the three week period starting Friday, December 24, 2010.

First up, the Moon. It starts the triple week in its waning gibbous phase, then passes through third quarter on Monday, December 27, as it makes the transition to morning's waning crescent. New Moon is hit on Tuesday, January 4, the Moon then moving into the evening sky as a waxing crescent that heads toward first quarter on Wednesday the 12th. At the end of our period, we get to see a bit of the waxing gibbous.

As it goes, the Moon first meets Saturn the night of Tuesday the 28th, gliding 8 degrees to the south of the ringed planet. Then watch as the waning crescent passes down and to the right of Venus New Year's Eve, and then celebrates New Year's day by joining up with the star Antares, after which it drops below Mercury. Finally, the waxing crescent appears several degrees northwest of Jupiter (and Uranus) the evening of Sunday the 9th, then to the northeast of them the following night. The Moon passes perigee, where it is closest to Earth, on Christmas Day, then apogee the night of Sunday the 9th.

The planets play their own games. After a long wait, Jupiter finally passes by Uranus on Sunday the 2nd, the two a mere 0.6 degrees apart, Jupiter to the south. Setting ever earlier, by 11 PM at the year's start, the giant plant nicely hovers in the western evening sky as darkness falls. For a time it is replaced by much dimmer Saturn, which by January 1 rises half an hour after midnight (shifting to midnight by January 9), still in Virgo, still to the northwest of Spica. Venus, brilliant in morning's light, makes a bigger splash. Rising before 4 AM, our closest neighbor passes greatest western elongation (48 degrees) with the Sun on Saturday the 8th. Mercury follows the next day, but at 23 degrees western elongation is far to the east of Venus and not far above the horizon during dawn. Not that anyone will notice, but Pluto goes through conjunction with the Sun on Sunday the 26th.

Four more events highlight our trio of weeks. First, the Earth passes perihelion, where and when it is closest to the Sun (91.41 million miles, 147 million kilometers, 1.7 percent below average) on Monday the 3rd. Obviously, distance to the Sun has nothing to do with the seasons (but every bit with the 23.4 degree tilt of its axis against the revolutionary perpendicular). Two days later, as a result of this tilt and the Earth's orbital eccentricity, we bottom out with the mid-northern hemisphere's latest sunrise of the season. Third, the new Moon will pass across the Sun for a partial eclipse. But don't look for it, as it is strictly a European/Asian/African event. Finally, you might watch for the Quadrantid meteor shower (named after the defunct constellation Quadrans, the Quadrant, which mostly lies in northern Bootes to the east of the Big Dipper's handle), which will peak around January 3-4. In a dark sky, you might see as many as one or two a minute.

Orion of course now dominates the late evening sky, its two brightest stars, Betelgeuse and Rigel, standing out like orange-red and blue-white jewels. To the northwest of Rigel find dimmer Cursa, the source of Eridanus, the celestial River, which ends far below northerners' southern horizon in brilliant Achernar.
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