SKYLIGHTS

Astronomy news for the week starting Friday, July 9, 1999.

This is the week of the new Moon, the phase reached the night of Monday, July 12 about the time of sundown in North America. Early in the week, the waning crescent will be nicely visible in morning twilight. The night of Tuesday the 13th the Moon will be only about 24 hours "old" and will appear as an extremely thin crescent in western twilight. Because the practical limit to lunar visibility is about 20 hours past new, it will at that time be difficult to see, but will easily be visible by the night Wednesday the 14th. The night of Thursday the 15th, the growing crescent will put on a nice show with brilliant Venus and the bright star Regulus in Leo, the three making a tight triangle with the Moon on top. Be sure to take a look. Perigee, when the Moon is closest to the Earth, occurs around midnight the night of Saturday the 10th, shortly before new, ensuring especially high tides at the coasts.

Venus's proximity to Regulus allows its motion against the starry background to be easily seen. The planet will pass 1.5 degrees to the south of the star the night of Monday the 12th, while the Moon is out of view. Just two days later, on Thursday the 14th, Venus will reach greatest brilliancy (magnitude -4.5) for its current evening appearance. As Venus circles the Sun inside the Earth's orbit, we see different portions of its daylight side, so it runs through phases like the Moon. When opposite the Sun, at superior conjunction, we see its daylight face and it is "full;" when it passes between us and the Sun, at inferior conjunction, which it will do August 20th, we see the nighttime side and it is "new." Because the planet is now getting closer to us, it also appears progressively larger. Greatest brilliancy takes place when Venus is a large rather thin crescent that can be seen in a small telescope at very modest power. Even binoculars will show it.

Scorpius, one of the few constellations that looks like what it is supposed to be, is now beautifully visible to the south just after dark. While the most southerly part of the ecliptic -- the winter solstice -- is in neighboring Sagittarius, Scorpius reaches the farthest south of any zodiacal constellation, the scorpion's tail just above the southern horizon for the middle US and out of sight for anyone above 47 degrees latitude. Mars, now moving quickly to the east relative to Spica in Virgo will enter Libra on July 26 and Scorpius on September 22, then pass just north of its namesake, Antares (meaning "like Mars," from the star's red color) on September 18.