Astronomy news for the week starting Friday, September 10, 1999.

This is an odd sort of lunar week for Skylights. The Moon's phase cycle is 29.53 days, so (barring variations caused by the somewhat non-circular lunar orbit) the average interval between quarters is 7.38 days, or just over a week. This particular week, from Friday through Thursday, just fits into that period, and as a result the Moon passes no major lunar phase positions; it passed new on Thursday, September 9, will hit first quarter the afternoon of Friday September 17, and will spend this week entirely in the waxing (growing) crescent. It will be just barely visible as an exceedingly thin crescent in western twilight tonight, Friday the 10th, and will be obvious by the next evening. Watch as it then passes the head of Scorpius up and to the right of Mars the night of Wednesday the 15th, then up and to the left of Mars and the star Antares the night of Thursday the 16th.

Mars, now low in the southwest as twilight nears its end, though bright, is difficult to see if there are any horizon obstructions. The red planet begins the week moving through Scorpius just to the east of the Dschubba, the central star of the Scorpion's head. On Tuesday, the 14th, it exits Scorpius and enters a long path through the non-zodiacal constellation Ophiuchus (the solar path, the ecliptic, passing through that constellation's modern boundaries). On the night of Wednesday the 15th Mars will make a very close pass (only 0.07 degree) south of the fifth magnitude star Rho Ophiuchi (which you will need binoculars to see). The star is famous for its proximity to a vast dark interstellar cloud in which star birth is furiously going on. The night of Thursday, the 16th, the planet will finally pass due north (about three degrees) of its similarly colored namesake Antares.

It is the eastern sky that now holds the real glories. Bright Jupiter is well up to the southeast of the Great Square of Pegasus by 10 PM, Saturn following close behind. Even binoculars (steadily held) will show some of Jupiter's bright moons. Dawn then brings even brighter Venus over the horizon. Though creamy white, the planet is so bright it can be seen very low above the horizon, where absorption by the thick air can give it a reddish cast. Even in bright twilight shortly before sunrise it is still quite visible. Well to the right of Venus shines the brightest star in the sky, Sirius, it and the other "winter constellations" slowly working their way toward evening as that season approaches.
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