Starry Skies Above Santa Monica

January 9-16, 2002

Mirek Plavec
Emeritus Professor of Astronomy,
UCLA

   The Day Is Getting Longer…
   …slowly, in the evening as well as in the morning.    The times of sunrise and sunset do not change symmetrically. The earliest sunset came on December 7, at 4:44 p.m. Since that day, the Sun has set later, slowly but steadily, and by Sunday, January 13, it will set at 5:05 p.m. – a gain of 21 minutes! On the other hand, the time of sunrise is the same (within one minute), at 6:59 a.m., from January 1 and 13, and only after that, it will start rising earlier, quite slowly at first.
   When the Sun was at its southernmost position, it shone, at the time of the local noon, directly above Sao Paulo, Brazil. This week, it will pass well north of Rio de Janeiro.

   Four Bright Evening Planets
   Well, they might count as four, since, in addition to Mars, Jupiter, and Saturn, the planet Mercury is also an evening star. However, I don’t think that it will be easy to spot. While the Sun is projected into Sagittarius, Mercury is in the next constellation of the zodiac, Capricorn. Its greatest angular distance from the Sun, 19 degrees, comes on January 11. Between January 9 and 13, Mercury will be quite bright, but can be easily lost against the fairly bright sky above the place where the Sun has set. During these four evenings, Mercury will set at 6:34 p.m., while the Sun will set about 90 minutes earlier. If you want to spot Mercury, start looking to the southwest by about 5:30. Mercury will shine a bit to the north of the point where the Sun has set. The Moon will pass below Mercury on the evening of Monday, January 14. However, it is questionable whether the Moon can help this time, since it will be an extremely thin crescent, just 1.5 days after New Moon, and therefore probably invisible. The chance of seeing Mercury is actually better on the earlier days (around January 10), since after that, Mercury rapidly fades in brightness. If you miss this opportunity to see Mercury, there will be a somewhat better one in late April/early May.
   Mars, shining in the constellation of Pisces (the Fishes), is currently projected almost exactly to the point the Sun reaches at the time of the spring equinox. Thus, Mars is no longer visible in the southwest as for many weeks before, but rather directly in the west. In that region of the sky, there is no competing bright star, and therefore Mars remains fairly prominent, shining as a typical star of the first magnitude, and its reddish color is still obvious. However, you must look fairly early, since Mars sets by 10 p.m.
   More conspicuous are the two big planets, Saturn and Jupiter, shining on the opposite side of the sky, above the eastern horizon in the early hours of the evening. The starry sky we see now in the evening is fairly rich in bright stars: at about 7 p.m., you can see 10 stars that qualify as true stars of the first magnitude. Saturn, by its brightness, surpasses all of them except one, namely Sirius. And Jupiter clearly outshines even Sirius.
   Where in the sky can you find these three brightest objects? At about 7 p.m. on any clear night, Sirius is low in the south-east, Jupiter is fairly high above the east, and Saturn is even higher, well above Jupiter. Saturn forms a fairly conspicuous close pair of bright 2 with Aldebaran, the “red eye of the Bull (Taurus).” Aldebaran is the fainter of the two. This rather striking pair of bright “stars” is 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”) shortly before 9 p.m.
   Rather strikingly bright is Jupiter, located in the middle of the constellation of Gemini (the Celestial Twins). Jupiter was exactly at opposition to the Sun on New Year’s Eve, and it still shines almost all the night. It culminates high above the south (almost overhead) by 11 p.m., and sets in the northwest after 6 a.m.
   Venus is invisible, on the other side of the Sun than we are, but the worst will be over just this coming week. Venus will be located exactly behind the Sun – in a position called the “superior conjunction with the Sun” on January 14, and after that, it will emerge as an evening star after sunset – but quite a few weeks will elapse before Venus really emerges from the Sun as an easily visible evening star.
   The Moon will be in its New Moon phase in the morning of January 13. It will then emerge in the evening sky after sunset as a thin crescent. It will pass below Mars in the evening of Friday, January 18, and even then, will still be a crescent – only about a quarter of its disk will be illuminated.

   Capella
   Last time I told you about two prominent winter stars: Sirius (in the southeast), which we see as the brightest real star, and Aldebaran, a red giant which currently forms a fairly conspicuous pair with Saturn. Today’s star, Capella, can also be found without a star map: on any clear evening, simply look for a bright yellow star that is almost overhead, well above both Saturn and Jupiter.
   By its surface temperature, Capella is similar to our Sun, but is bigger: a yellow giant – well, actually two yellow giants very close to each other. They are so close to each other that no telescope resolves them – only a spectrograph told astronomers that here are two similar giants orbiting a common center of gravity in a period of only 104 days. The discovery was made at Lick Observatory, near San Jose, in 1899. Capella is probably about 41 light years distant, and emits about 150 times more light than the Sun. One more curiosity: the name Capella is Latin, and means “little nanny goat.” A fancy name for a star!