Astronomy news for the week starting Friday, January 14, 2000.

The Moon reaches first quarter at the start of the week, Friday January 14, and then waxes through gibbous to full next Thursday the 20th. It will be found to the southeast of Jupiter the night of Friday the 14th and to the southeast of Saturn the following evening. Less than two days before full, it passes perigee, where it is closest to the Earth.

The big lunar news, however, is a total lunar eclipse the night of the full Moon, Thursday the 20th. Since the Earth's long shadow is directed opposite the Sun, like the Sun it falls on the ecliptic (the apparent annual solar path). Lunar eclipses can therefore take place only when the Moon is full and is on or near the ecliptic. Because of the tilt of the lunar orbit, the full Moon usually passes above or below the Earth's shadow, but this time it will plunge right through it. The timing is near-perfect for North America, allowing everybody to watch. The Moon will enter the dark part of the Earth's shadow at 9:01 PM CST, and becomes fully immersed at 10:05 PM. Mid-eclipse, when the Moon is darkest, occurs at 10:44 PM, the Moon leaves the dark shadow at 11:22, and the show is over at 12:25 AM. Subtract two hours for PST, add one for EST. The shadow is not perfectly dark, as it is illuminated by sunlight playing off the Earth's atmosphere. As a result, the eclipsed Moon does not disappear, but takes on a dark reddish color. Its brightness depends on the transparency of the air, and therefore on cloud cover and particularly on how much contamination there is from volcanic eruptions. At this eclipse, the Moon will pass south of the center of the shadow, and at mid- eclipse you can see a gradation in brightness from south to north. The changing colors are quite attractive. Though easily seen with the naked eye, the best view is with binoculars. During the partial-eclipse stage, note the circular outline of the Earth's shadow, the first real proof, known since ancient times, that the Earth is a sphere.

While checking the early evening sky, be sure to note Mars, still low in the southwest. Venus is still dominating the southeastern morning sky, while little Mercury is entirely out of sight, passing through superior conjunction (on the other side of the Sun) on Saturday the 15th. While the full Moon is darkened during the eclipse, note its placement midway between Gemini and Cancer, Gemini's Castor and Pollux pointing right at it. The Moon moves by its own diameter in an hour, and these background stars make the motion easy to see.
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