Starry Skies Above Santa Monica

January 16-23, 2002

Mirek Plavec
Emeritus Professor of Astronomy,
UCLA

   Three Bright Evening Planets
   Mars, shining in the constellation of Pisces (the Fishes), is currently projected almost exactly to the point which the Sun reaches at the time of the spring equinox. Thus, Mars is now visible 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, fits among them, but Jupiter outshines even the brightest star, 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 objects 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”) by about 8:20 p.m. After that, you must look for them in the west, where they set after 3 a.m.
   Rather strikingly bright is Jupiter, located in the western part of the constellation of Gemini – on the opposite side from the two bright stars, Castor and Pollux. When the sky gets sufficiently dark, say after 6 p.m., Jupiter dominates the eastern sky. It culminates high above the south after 10 p.m., and after that, you must look for this very bright planet in the western part of the sky.
   The only star that can compete with Jupiter in brightness is Sirius, which shines down there in the southeast, and culminates in the south around 11 p.m. Venus is now nominally an evening star – it moved to the east of the Sun on January 14, and therefore will now be setting in the west after sunset, but its angular distance from the Sun is quite small: on Wednesday, January 23, Venus will set only 7 minutes after the Sun! Hopeless! We must wait for a few more weeks to see this famous Evening Star.
   The Moon was in its New Moon phase in the morning of January 13. It then emerged 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, it will still be a crescent – the First Quarter, with one half of the Moon’s disk illuminated, comes on January 21.

   Look for the Southernmost Star!
   I will start with a small dose of geometry, knowing that all of you loved mathematics when you were school kids! In the unlikely case that you hated it, you may skip down to the paragraph that starts with “The second brightest star…”
   The zenith, the point in the sky that is exactly above your head, is 90 degrees from the horizon – the ideal horizon with no mountains or other terrestrial obstacles. We live at the northern latitude of 34 degrees, which also means that our zenith – the point on the celestial sphere that is exactly above our head – is 34 degrees above the celestial equator (which is the projection of the terrestrial equator upon the celestial sphere).
   On our January evenings, it is easy to see where the celestial equator is: it is marked by the “three in a row” – the three bright (second magnitude) closely spaced stars that mark the belt of Orion. These stars are 90 - 34 = 56 degrees above the southern point of the horizon at about 9:20 p.m. (and come there 4 minutes earlier every following night). The brightest star in the sky, Sirius, lies approximately 17 degrees below the celestial equator, so when Sirius culminates (currently at about 10:30 p.m.), it is located 39 degrees above the southern horizon.
   The second brightest star in the sky is called Canopus. It lies much farther down in the south than Sirius — 52.7 degrees below the equator! — but you have a good chance to see it just now! Look down deep, well below Orion and below Sirius, just about half-way between the two, and look at about 10:10 p.m. You have no more than one hour on each side of this time, and you must look from a place from which you can see all the way down to the horizon – so look either from the seashore where it faces the south, or from the mountains above us!
   OK, so all this takes a definite effort. Is it worth it – just to see a star? I think it is: Sirius, easily visible from here, actually passes overhead so far south that it passes overhead at La Paz or the city of Brazilia. However, Canopus is so much farther down that it passes overhead at Punta Arenas, at the southernmost bottom of South America! So, try to spot Canopus, and next time, I will tell you more about this star!