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Photo of the Week. Great Orion rises from his slumber, the reddish Orion Nebula just clearing the trees.

Astronomy news for the week starting Friday, December 14, 2007.

We start, as always, with the ever-popular Moon, which begins the week well along in its waxing crescent phase. Passing first quarter on Monday the 17th, it then enters the waxing gibbous as it heads toward full next week. On Sunday the 16th, the Moon will pass north of Uranus, which still hangs out in eastern Aquarius to the southwest of the Circlet of Pisces.

Four planets plan big events. At the bottom of the list is Pluto, which passes conjunction with the Sun on Thursday the 20th, making it REALLY invisible. Next up is Mercury, which also passes conjunction with the Sun, on Monday the 17th. Given its position inside the Earth's orbit, it (like Venus ) can go through two kinds of conjunctions, one when it is between us and the Sun, an "inferior conjunction", the other (like this one) when it is on the other side of the Sun, a "superior conjunction." Saturn then comes forward by entering retrograde, or westerly, motion against the stars on Thursday the 20th, as the Earth prepares to swing between it and the Sun. Watch for the ringed planet's rising in southern Leo around 10:30 PM.

The week, indeed the rest of the year, however, really belongs to Mars, which in this orbital round makes its closest approach to the Earth on Tuesday the 18th, when it is 0.589 Astronomical Units (88.2 million kilometers, 54.8 million miles) away. It is also then at its brightest, just a hair brighter than the brightest star, Sirius. Mars reaches opposition with the Sun on December 24th. That closest approach does not occur at opposition is the result of Mars's rather eccentric orbit. Near opposition, the red planet now rises in southwestern Gemini just after sunset and crosses the meridian high to the south about half an hour after midnight.

All of this activity is watched by far-brighter Venus, who still brilliantly glorifies the southeastern morning sky, rising just before 4 AM. And by Comet Holmes. Still in Perseus, it remains a nice binocular object.

It's more than past time to note the rising of Orion, who lofts himself above the eastern horizon as twilight draws to a close. Look for his three star belt and the two first magnitude supergiants, Betelgeuse, to the northeast of the belt, and Rigel (actually zeroth magnitude) to the southwest.
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