SKYLIGHTS

Astronomy news for the period Friday, May 7, through Sunday, May 16, 1999.

This Skylights will cover the period through Sunday, May 16. The Moon passes its last quarter early in the week, on Saturday, May 8, about noon Central Time, close to the time of moonset. It will then wane in the morning hours through the crescent, finally passing new on Saturday the 15th, perigee (the closest approach to the Earth) taking place only three hours later. Just before the quarter, as it moves against the stars of Capricornus, the Moon passes over both Uranus and Neptune. Neptune, to the west of the Uranus, is occulted first, on Friday the 7th, while Uranus, a dozen degrees to the east, is occulted on Saturday the 8th, only an hour before the quarter phase is reached. Unfortunately, neither of the events is visible in North America as they take place during daylight. But at least we will know what is happening. Later in the week, on the morning of Thursday the 13th, the Moon will be found to the southeast of bright Jupiter, which is now beginning a morning appearance, rising to the east in twilight among the stars of Pisces.

The planetary evening sky is now dominated by bright Mars and far more brilliant Venus. Mars, which passed opposition to the Sun in late April, is now rising before sunset. The red planet is tilted so that in a telescope we see the north polar cap, which contains a great deal of water ice. Visible only with difficulty in large telescopes are the two Martian satellites. Just 20 or so kilometers in diameter, they are probably captured asteroids. Mercury and Venus have no known satellites, and the Earth's was probably formed in a giant collision with a planetary interloper about the size of Mars very early in the Solar System's history. Only the outer planets have "natural" satellites that were born with the planet, Jupiter 16 (though the outer eight may also be captured), Saturn perhaps 20, Uranus almost as many, Neptune but a handful, the largest, Triton, again captured.

The ancients populated the sky with great heroes and other mythical figures. Many of the spaces between them were filled in during the 17th and 18th centuries with a variety "modern" constellations that represent artifacts of the times. Look about 10 degrees directly below Regulus in Leo to find the brightest star of Sextans, the Sextant, cousin to Octans the Octant of the southern hemisphere and the now-defunct Quadrans the Quadrant, all navigational devices. Farther south, skimming the horizon from mid-northern latitudes, is all-but-invisible Antlia, the Air Pump. If we were to invent the constellations now we would probably see television sets and running shoes.