Starry Skies Above Santa Monica

December 26 - January 2, 2000

Mirek Plavec
Emeritus Professor of Astronomy,
UCLA

   The Slowly Changing Sky
   The starry sky changes very slowly from week to week. Each constellation rises, culminates or sets 4 minutes earlier every night. That’s a fairly slow change! It amounts to about half an hour per week. The planets do move with respect to the stars, but that motion is again rather slow. Mercury is an exception, but it remains so close to the Sun for most of the time that it is difficult to see. Even Copernicus confessed that he had never seen Mercury! The fastest moving object is, of course, the celestial body nearest to us, namely the Moon. However, even for the Moon, the phase change from one night to the next is usually not striking for the casual sky watchers. Thus, for example, the Moon appears to be Full for at least three consecutive nights. You can test it this week! The Moon will be exactly full in the pre-dawn hours of the night of December 29/30, which is Saturday night. Yet it may appear full from Friday through Tuesday or even Wednesday.
   Yes, there are occasional sudden changes in the sky. A lone meteor, or an occasional meteor shower – but these are atmospheric phenomena, not the real universe. A nova or even a supernova may suddenly flare up brightly – but such an event is very rare. One of them is long overdue! And so is a really bright comet! Perhaps if we jointly make a proper New Year’s wish…

   Where the Planets Are
   On Sunday evening, the Sun will set at 4:53 p.m., and at about 6 p.m. the sky will be sufficiently dark to show you the stars, if clouds and city lights permit. By that time, Mars (in Aquarius) will be above the southwest (it will set after 10 p.m.). Although the greatest glory of Mars is long past, the planet is still fairly bright, and without competition in the southwestern part of the sky.
   Conspicuous are the two big planets, Saturn and Jupiter. Saturn shines as a bright star of the first magnitude, but is not really striking. What will help you identify Saturn is the close pair of bright objects that Saturn forms with Aldebaran, the “red eye of the Bull (Taurus).” Aldebaran is the fainter of the two. This rather striking pair of bright “stars” is fairly high above the east in the early evening, and culminates high above the south (you may have the feeling that the two objects are “almost overhead”) before 10 p.m.
   Rather strikingly bright is Jupiter, located in the middle of the constellation Gemini (the Celestial Twins). When it becomes visible against the darkening sky, Jupiter is in the northeast, and then culminates high above the south at midnight. Thus Jupiter stands, in our sky, just opposite to the Sun, and, indeed, the time of its opposition to the Sun comes on the very last night of the year 2001. The next brightest object in the sky is a real star, namely Sirius, which rises in the southeast at about 7 p.m.
   Venus, in spite of its brightness, is too close to the Sun to be visible. Mercury sets, in the southwest, about one hour after the Sun, and would be difficult to find against the bright background of the sky after sunset.

   The Moon Occults Saturn
   Naturally, when the Moon is above the horizon at night, it is much brighter than all the other objects, planets or star alike. This will be the case this coming week. Tonight, Wednesday, December 26, the Moon will appear nearly full, and, rising, it will precede the bright pair of Saturn and Aldebaran. Then, on the next night, Thursday/Friday, the Moon will actually pass in front of Saturn – there will be an occultation of Saturn! The planet disappears behind the (thin) dark part of the Moon 19 minutes after midnight, and will emerge at 1:35 a.m. Since Saturn is sufficiently bright, you will be able to observe this (fairly rare) occultation with the naked eye, although binoculars would be very useful. And, if you have access to a telescope, you would be able to see Saturn’s rings disappearing and then reappearing again! All this will happen high in the sky above the south-west, and the only disadvantage, for most people, is the time of the event.
   On the nights of December 29 and 30, the Moon will be seen fairly close above Jupiter. Since both object are very bright, it will be a good show, although lacking the drama of an occultation. On that night, after midnight, the Moon will be perfectly full.
   When our Mrror week ends, on January 2, the Moon will be near the first-magnitude star Regulus in the constellation of Leo (the Lion), and will still appear very nearly full.
   And if you managed to read all the way down to here, then you certainly deserve my wish: Have a Happy and Healthy New Year 2002!