Astronomy news for the week starting Friday, July 7, 2000.

One wishes for some celestial action this week, but there is precious little. Will the Galaxy (seen by us as the Milky Way) perhaps cooperate and produce an exploding star? Likely not. Instead we are left with the Moon going through its first quarter on Saturday, July 8th, and that is about it. The event that will take place about the time North and South Americans rise for the day, before the quarter rises around noon.

After sundown, admire the quarter set within the stars of Virgo, the Moon just up from the bright star Spica. Of the five first magnitude stars of the Zodiac (Aldebaran, Pollux, Regulus, Spica, and Antares), Spica is number two in proximity to the ecliptic, the apparent path of the Sun. (Regulus, only a half a degree north of the ecliptic, the angular diameter of the Moon itself, is the winner. Spica is two degrees to the south of the ecliptic). As such, Spica is regularly covered, or occulted, by the Moon on its monthly path around the Earth. Note the position of the quarter Moon now. Because of the orbital motion of the Earth around the Sun, the next first quarter will take place a constellation over to the east, smack within the stars of dim Libra. All the phases so move around the Zodiac over the course of the year.

The lunar orbit is tilted by about 5 degrees to the ecliptic, so it can be found as much as 5 degrees north of the path and as much as 5 degrees south of it. Moreover, the orbit "wobbles" with an 18.6 year period (The effect is called the "regression of the nodes, as the "nodes," the points where the Moon crosses the ecliptic, move backward around the ecliptic with the same 18.6 year period.) Though the Moon is now passing north of Spica, in 10 years, it will pass to the south. Over the nearly two decades of the regression, the lunar disk will occult all stars within 5 degrees of the solar path. Astronomers love such occultations, as they can determine the size of a star from how long it takes it to disappear behind the lunar disk, and can also check for close companions.

Of course the sky does not have to DO anything to be wonderful to watch. Simply admire stars and planets for what they are, admire their passage across the celestial vault. Watch Jupiter and Saturn rise against the dark eastern sky, look at great Scorpius on the meridian at 11 PM, see the Milky Way, the combined light of the billions of stars of our Galaxy, pass overhead near midnight, the center of the Galaxy set within the confines of Sagittarius.
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