Astronomy news for the week starting Friday, January 12, 2001.

The week begins with the Moon in its waning gibbous phase. Passing third quarter the morning of Tuesday the 16th about the time of sunrise, it finishes the week as a waning crescent. The morning of Wednesday the 17th finds the Moon to the northwest of Mars (now in Libra), the morning of Thursday the 18th to the northeast of the red planet.

The week belongs not to Mars or the Moon, however, but to Venus, which reaches greatest eastern elongation from the Sun shortly after it sets the night of Tuesday the 16th. "Elongation" is the angle that any planet makes with the Sun. Venus, closer to the Sun than we are, can never get more than 47 degrees from the Sun, its maximum angle. The planet thus achieves its greatest visibility this week. Since it is now at the tangent point in its orbit as seen from Earth, it will (through the telescope) also appear as the quarter moon does in the sky, one half seen in sunlight, the other half in darkness. From here on to conjunction with the Sun on March 29, the planet will appear as an increasingly thinner crescent. At the same time, it is approaching the Earth and appearing ever-larger, and thus brighter, maximum brilliancy to be reached on February 21. Though the angle between the Sun and Venus will now decrease, since the Sun is moving northward along the ecliptic and is setting later, Venus will continue to set later as well until early February, the "evening star" quite dominating the early night sky.

At the other end of the planetary spectrum, Mercury passes conjunction with Neptune (Mercury two degrees south) on Saturday, the 13th, the solar glare causing the event to go unseen. In between, the early evening eastern sky is dominated by Saturn and Jupiter, both still retrograding (but not for long) in Taurus. The three planets, Venus, Saturn, and Jupiter, act like a dotted line in the sky that to a good approximation shows the ecliptic and the path the Sun will soon follow as northern winter wanes and turns to spring.

Look to the southeast around 8 PM to see Orion climb the sky. To the right, on the meridian to the south, winds dim Eridanus, the celestial River that represents the "River Ocean" of classical times. From modest Cursa, just northwest of Rigel in Orion, Eridanus flows west, and then curves south below the horizon of northern latitudes, ending in brilliant Achernar, which can be seen only south of 32 degrees north latitude. High above, the Pleiades, the Seven Sisters star cluster, crosses the meridian as well. Most eyes see 6 stars, but those with sharper vision might catch 8 or even more, the view richly enhanced by binoculars.
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