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Astronomy news for the two weeks starting Friday, January 22, 2010.

This seems to be a fine period of time for astro-things starting with the letter "M." First, we have the good old Moon, which begins our fortnight at first quarter on the morning of Saturday, January 23rd. After passing through its waxing gibbous phase, it rolls by full (and Mars, but more about that later) the night of Friday the 29th, after which it wanes through most of its gibbous phase as it approaches third quarter the night of Friday, February 5. It also passes perigee, where it is closest to Earth, on Saturday the 30th. Then the night of Tuesday the 2nd, the Moon can be seen passing well south of Saturn. Finally, the night of Thursday the 4th, look for the Moon to the southwest of Spica.

Then there is Mercury, which passes its greatest western elongation, 25 degrees to the west of the Sun, on Tuesday the 26th. Look to the southeast in morning twilight for a bright "star." At its best, the little planet is amazingly visible, and then, like Santa Claus, with a nod, it turns and disappears.

But not the number three "M." This fortnight, "M" is really for Mars. On Friday the 29th, the red planet goes through opposition with the Sun, when it rises at sunset, sets at sunrise, and passes highest on the meridian at midnight. As the Earth passes it in orbit (between Mars and the Sun), Mars is also thus moving fastest in angle to the west against the stars, and by the time of actual opposition is well back into the constellation Cancer to the east of the Beehive Cluster. Two days before opposition, the planet comes closest to the Earth on this orbital round (opposition and closest approach not the same because of the oblateness of the Martian orbit), when it will be 61.7 million miles (99.3 million km) away, nearly 1.8 times the closest that is possible (and that was achieved at the truly "favorable opposition" that took place in August of 2003). At Mars's current brightest, it shines about as brightly as the top-level stars. Then to wrap up this portion, look for two of the "M"s to get together, as the full Moon passes seven degrees to the south of Mars the night of Friday the 29th.

Switching letters of the alphabet, Jupiter is still with us, though not for long. Look for it in the southwest early in the evening, as the giant planet sets about as twilight draws to a close. Saturn is much better situated. Lying between Regulus and Spica just five or so degrees to the east of the Autumnal Equinox, the ringed planet now rises due east in mid-evening, around 9:30 PM.

Earth rings in a bit, as on Tuesday the 2nd we celebrate a "cross- quarter day" that lies halfway from the first day of winter to that of spring, in North America called "Groundhog Day." Yes, it's an astronomical holiday, the Sun halfway between the Winter Solstice and the Vernal Equinox. Time to party as we slowly leave winter behind. Others are May Day Eve and Halloween.

Northern hemisphere winter presents us with a wonderful stack of first magnitude stars. Look between 9 and 10 PM and start with Auriga's Capella in the far north, then drop through Pollux (add neighboring Castor, both of Gemini), Aldebaran of Taurus (seen against the Hyades), Betelgeuse and Rigel of Orion with Procyon (in Canis Minor) to the left, then on to the sky's brightest star Sirius (Canis Major), and if you are far enough south, to number two Canopus, the luminary of ancient Argo, the Ship.
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