Starry Skies Above Santa Monica

March 1-8, 2001

Mirek Plavec
Emeritus Professor of Astronomy, 
UCLA

   Sun, Moon and Planets
   The Sun continues to move upward through Aquarius (the Water Bearer), and is now only 6 degrees below the equator. On Sunday, March 4, it will pass, at the local noon, very close to the zenith of the islands Zanzibar and Bougainville, over Jakarta, Kinshasa in Zaire, and over Natal in Brazil. For us, the Sun will rise at 6:18 (a gain of 8 minutes per week) and set at 5:52 p.m. (6 minutes later than a week ago) -- so, again, a net gain of 14 minutes of daylight time.
   The Moon reaches its First Quarter on Friday, March 2, will then grow more and become Full on Friday, March 9. On the evening of Thursday, March 1, the Moon will shine just below Jupiter and Saturn. The First Quarter Moon will lie already to the east of Aldebaran in Taurus, and the Full Moon will be projected on the boundary between Leo and Virgo.
   Venus is still very prominent every evening, visible fairly high above the western horizon already by 6:20 p.m. or so. It still shines quite long, and sets by 8:33 p.m. If you compare the time of setting with the previous Sunday, you will notice that Venus sets 17 minutes earlier than last Sunday, while the Sun sets 6 minutes later. The fact that Venus is returning to the Sun (as seen in our sky, i.e. diminishing its angular deviation eastward of the Sun) is beginning to show, still rather inconspicuously. This is partly due to the fact that Venus is currently projected fairly high above the ecliptic, so that it lies 19 degrees higher to the north than the Sun. As a consequence, Venus still remains prominent and fairly high in the sky shortly after sunset.
   When the sky gets still a bit darker, you will have no problem in finding the bright Jupiter to the southwest of the zenith. Saturn, fainter (but still a first-magnitude "star") is not far to the west of Jupiter. Both planets now move eastward among the stars, but at a snail’s speed, so you will find them pretty much at the same place where they have been for weeks. Currently, they are fairly close to each other, Jupiter still between the Pleiades and Aldebaran, and Saturn not far from Jupiter, a few degrees to the west. It is the motion of the Earth, as reflected in the apparent motion of the Sun, that changes their visibility: by midnight, both planets disappear below the western horizon. 
   The only planet visible in the morning hours is therefore Mars, which rises deep in the southeast about half-an-hour after midnight, and culminates above the south by 5:30 a.m. Mars, being much closer to the Sun and to us than are Jupiter and Saturn, appears to move definitely faster with respect to the stars. It is currently passing a few degrees above its competitor in color, the red supergiant Antares. For the ancient Greeks, the god Ares had the same disgusting functions as had Mars for the Romans: war, fire, destruction. Since the bright star in Scorpius competed with Ares in reddish color, and often also in brightness, it got the name Anti-Ares, or Antares. As Mars is gradually approaching the Earth, it gains in brightness, and currently is already winning the competition with Antares.

   Two Planets Meet 
   – Rather Secretly
   It would be hard to imagine two planetary worlds more different than Mercury and Uranus, one moving close to the solar fireplace and the other far in the dark and icy space. On March 10, they will meet in the sky: Mercury will pass less then 10’ (arc-minutes, i.e. about 1/3 of the Moon’s disk) south of Uranus. It would be a good opportunity to locate and identify Uranus, which is visible in binoculars -– if it were not for the fact that both planets rise late, just at 5 a.m., when the Sun already begins to illuminate the upper atmosphere above our heads, and will soon obliterate the stars.
   Mercury will be 138 million km from us, while Uranus will be by almost 3,000 million km distant. In spite of that, the apparent disk of Uranus will still be half the size of the apparent disk of Mercury – but both are quite small (Mercury 7" in diameter). The encounter will occur in the constellation of Capricorn.
   Mercury was known to our ancestors from times immemorial, in spite of its proximity to the Sun. From places where the first advanced civilizations flourished, it was not difficult to spot Mercury for a few weeks every year. The farther to the north one goes, the more difficult it is to see Mercury. Mikolaj Kopernik, who lived at latitude 54 degrees, complained bitterly that he had never seen Mercury…
   On March 13, 1781, that is, 220 years ago, Uranus entered human history. William Herschel, a musician in Bath, England, became interested in astronomy in 1772, and began building better and larger telescopes. Where many an amateur astronomer stops, Herschel started: after completing a satisfactory telescope, he began to study the entire starry sky -- he actually scrutinized one star after another! 
   Then, on March 13, 1781, Herschel reached the constellation of Gemini, and there he spotted an object that was not point-like as all stars are: it was a tiny disk. Repeated observations on the following nights showed that the object was moving against the background stars. Herschel at first suspected a faint comet, but subsequent observations indicated a nearly circular orbit around the Sun, at a distance about 19 times larger than our distance from the Sun. To a great surprise of all astronomers, it was a planet --- all of a sudden, the solar system of planets became very much larger!