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Photo of the Week.The Sun gently sets through distant ocean clouds.

Astronomy news for the week starting Friday, February 20, 2009.

The Moon starts us off with its waning crescent phase, which always makes for a pretty morning sight. The waning crescent ends with the new Moon on Tuesday, February 24, after which it reverses itself to appear as a waxing crescent in the early evening sky. Your last glimpse of the waning version will be in twilight the morning of Monday the 23rd, while the first sighting of the waxing crescent might be had, also in twilight, the evening of Thursday the 26th.

The twilit morning of Sunday the 22nd, the Moon will make a remarkable, though difficult-to-see, quartet along with Mercury, Jupiter, and Mars, all running down and to the left. The sight will require a flat, clear horizon and binoculars. By the following morning, the Moon will have moved to the other side of the planetary trio. Formal conjunction between the Moon and Mercury takes place on Sunday the 22nd, as does that with Jupiter, while the conjunction between the Moon and Mars waits until the next day. On Monday the 23rd, Mercury then passes about half a degree south of Jupiter. Looking ahead a bit, so as to prepare, by far the best sight will be the close pairing between Venus and the waxing crescent Moon the evening of Friday the 27th.

Venus, of course, remains a striking sight in western evening twilight. Still near maximum brilliance amidst the faint stars of Pisces, it stays up until around 9 PM. Vying for attention on the other side of the sky, Saturn, still in southeastern Leo, rises about two hours earlier, crossing the meridian to the south around 1 AM. Through the telescope, the rings have flattened out and you can see how very thin they are. At the crossing of the ring plane, they quite disappear from view.

Spotted Comet Lulin yet? It's visible in binoculars moving to the northwest between Spica in Virgo and Regulus in Leo. The night of Tuesday the 24th, it will pass south of Saturn.

We can divide the constellations into two broad groups, the 48 ancient ones, whose origins are largely lost to time, and the 38 moderns that were invented largely between the years 1600 and 1800 (with Argo broken into three giving us a total of 88 accepted figures). Unique among them is Eridanus, the River, which is a hybrid of the two. Starting at Cursa (just northwest of Rigel in Orion), the ancient part of the stream winds west, then bends south before twisting east then west again, whereupon it ends at Acamar (Theta Eridani). Once the deep southern stars were seen and mapped, astronomers then added a "modern" portion that extended the running river from Acamar to first magnitude Achernar (Alpha Eri), which can be seen only below about 32 degrees north latitude, which includes the extreme southern continental US and Hawaii.
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