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

Marshmallow clouds

Photo of the Week. Marshmallow clouds drift beneath a pale sky.

Astronomy news for the week starting Friday, December 30, 2005.

'Tis the year's end, and a Happy New Year to all, as this Saturday night the clock rolls over to 2006. The year ends, and Skylights' week begins, with the new Moon on Friday, December 30, giving us a reverse "blue moon" effect (wherein there are two full moons in a month), December 2005 having two NEW Moons. The rest of the week is spent with the Moon in its waxing crescent phase. In celebration of the new year you can get your first look at the Moon the night of Sunday, January 1, when it will appear low in the southwest in twilight to the left of Venus, the brilliant planet now setting ever earlier in twilight and rapidly disappearing from view. Early in the lunar cycle the nighttime side of the Moon will be bathed in Earthlight. On Monday the 2nd and Tuesday the 3rd, the Moon will respectively (and invisibly) pass to the south of Neptune and Uranus.

As Venus vanishes, the early night sky is taken over by Mars (still in Aries), which transits the meridian to the south just before 8 PM, and Saturn (yet in Cancer), which rises about an hour earlier. Though Mars has faded some from its earlier glory, it still shines at the minus first magnitude, and is brighter than all but the two brightest stars, Sirius and Canopus. Saturn (at magnitude zero brighter than all but the top three stars, number three Alpha Centauri) then transits the meridian at 2 AM, followed nearly an hour later by the simultaneous setting of Mars and the rising of Jupiter, whose glowing brightness no star can match. Now in western Libra, Jupiter falls well to the east of Virgo's Spica.

Far fainter, the asteroid Vesta (the fourth discovered), will pass through opposition with the Sun on Thursday the 5th. At faint sixth magnitude in central Gemini, it is just barely visible to the naked eye (given excellent vision in a dark location), making it unique among such bodies (the asteroids a collection of planetary debris mostly between Mars and Jupiter).

Meteor showers come from the debris of comets, not asteroids. Keep your eye out for one of the major showers of the year, the Quadrantids, which peak the morning of January 3, and that come out of the defunct constellation Quadrans, which lies near the Big Dipper.

On New Year's Day, the Moon will pass through perigee, where it is closest to the Earth. Just three days later, at about 9 AM CST on Wednesday the 4th, the Earth then passes through perihelion , where it is closest to the Sun, 147 million kilometers (91.4 million miles), 1.7 percent closer than average. Since perihelion takes place in the heart of northern winter, solar distance clearly plays no significant role in the seasons, which are caused by the 23.4 degree tilt of the Earth's rotational axis relative to its orbital axis. Since ocean tides depend on the inverse cube of the distances between the Earth and the Moon and Sun, they will be especially high (and low) at this new Moon. Tides slow the Earth's rotation, and to synchronize clocks with precisely-kept "atomic time," a "leap second" will be added at midnight as the Old Year passes to the New (giving 61 seconds to the last minute).

Orion and his cohort of bright constellations are now making a serious impact on the nightly sky, Sirius in Canis Major rising as twilight ends. Watch for them as they cross the sky during the wintery nights. Meanwhile in the northeast, the Big Dipper is rising. The Little Dipper, however, is at its low point beneath the ever-constant pole.
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