Astronomy news for the week starting Friday, September 15, 2000.

The Moon, now past full and in its waning gibbous phase, heads toward its third quarter, the phase reached the evening of Wednesday, the 20th, before moonrise in North America. Because the Sun will be just one day shy of passing the Autumnal Equinox in Virgo, which will mark the beginning of northern hemisphere autumn, this third quarter will be near the Summer Solstice in Gemini, and will be the highest (and earliest-rising) third quarter of the year. As the phase wanes, the Moon will make interesting configurations with the two giant planets; it will be just beneath Saturn the night of Monday the 18th and down and to the left of Jupiter the following night, Tuesday, the 19th.

The past couple months have been dominated by these two largest members of the Solar System (ignoring the Sun of course) as they slowy invade the evening sky, Saturn now rising arund 10 PM, bright Jupiter shortly thereafter, both engagingly set amidst the stars of Taurus. Now it is time to highlight the two planets most like the Earth, Venus, on the sunward side of our planet, Mars the next one out. Both are now clearing daylight and becoming visible, Mars in the morning, Venus in the evening. Mars, in Leo, now rises almost due east shortly before 5 AM. In contrast, Venus can be seen low in the west-southwest in evening twilight, setting as twilight fades. Curiously, they each make passes at the two first magnitude stars that flank the Autumnal Equinox and that now therefore flank the Sun. On the night of Monday the 18th, Venus will be about 3 degrees north of Spica in Virgo, and on the morning of Saturday, the 16th, Mars will be only a degree north of Regulus in Leo (the first magnitude star closest to the ecliptic, the apparent path of the Sun). While brilliant Venus far outshines Spica, Mars, almost as far away from us as it can get, and now only second magnitude, takes a back seat to Regulus. The star provides a good reference with which to watch Mars's rapid movement to the east against the stellar background as the Earth very slowly begins to catch up with it.

The Moon leaving the evening sky allows the admiration of the rising autumn constellations. By 10 PM, that great harbinger of fall, Pegasus, its Great Square rising like a giant diamond, is fully visible in the east. To the left runs a string of stars that makes part of Andromeda, and climbing the northeast is the "W" of Cassiopeia, rising as the Big Dipper falls in the northwest. As the night rolls on, follow the western side of the Great Square southward to find the bright star Fomalhaut in Piscis Austrinus, the Southern Fish, the star (for most people in North America) tracking a lonely path not far above the southern horizon.
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