The moon: The four-day-old crescent moon of Dec. 1 is in Capricornus, growing to first quarter on Dec. 4. The moon is in Taurus when it is full on Dec. 10-11, and the bright reddish star to its right is Aldebaran. On the night of the 12th the gibbous moon is below the stars Castor and Pollux in Gemini, and on the 15th it passes above Regulus, in Leo. Last quarter moon is in Libra on the 18th, located just above the Autumnal Equinox when it rises about midnight on the 17 th. The waning crescent passes Mars on the 18th, Saturn and Spica on the 19th, then Jupiter on the 21st, and it will be seen near them in the morning sky for several days. After new moon early on Dec. 26, the crescent moon of the new cycle should show up in the evening sky by the night of the 28th, when it passes near Venus.
Stars and Planets: Mars, Saturn, Spica, and Jupiter, rising in that order from midnight on, offer a spectacular show in the morning sky, although Jupiter's motion to the east has stretched November's triangle out quite a bit. Look for them from about 4 a.m., when they should be well clear of the horizon's murk, until dawn wipes them out. Note that Jupiter has now shifted well to the left of Virgo's bright star Spica, while Mars is moving swiftly toward both Saturn and Spica. Saturn, meantime, has pulled much closer to Spica, but hasn't yet passed to its left. It will pass it in early January, and then again in late February, and then again in September 1982, and then not for another 30 years! Can you guess why? I'll tell you about it in January. Mercury was part of the Saturn, Spica, Jupiter scene last month, but it has stayed close to the sun (actually moved closer to it) while moving rapidly away from Virgo. On Dec. 10, Mercury passes the sun, on the far side of it as seen from earth, in the position called superior conjunction. The planet then enters the evening sky, but remains too close to the sun (setting very soon after sundown) to be seen for the rest of December and early January.
Dec. 4: The first quarter moon is just below the Square of Pegasus, four stars arranged like a box oriented north-south and east-west. The two sides of the Square point nearly to the North Star (Polaris).
Dec. 10: The full moon identifies Taurus for you tonight. The bright star near the moon is Aldebaran, with a ''vee'' of stars nearby to mark the Bull's face (the stars are part of the Hyades cluster).
Dec. 10-11: Perigee moon (nearest earth) occurs late on the 10th, full moon early on the 11th (nine hours later). Tides will be exceptionally strong on the 11th as the effect of perigee adds to the normally stronger spring tide that accompanies syzygy twice each month (at full and new moon).
Dec. 13-14: The normally productive Geminid meteor shower, one of the two best of the year, reaches maximum tonight. But since the full moon occurred only two nights ago, the still bright waning gibbous moon will obscure all but exceptional objects. Unfortunately, the Geminids seldom produce bright meteors, unlike the equally strong Perseids of August.
Dec. 16: Venus is at greatest brilliancy in the evening sky. The planet is now in the part of its orbit that takes it swiftly from left to right. This has two opposing effects on its brightness. As it approaches earth, it grows larger and brighter. But as it moves between earth and sun, less of its bright (sunlit) surface faces earth. The best balance occurs today, and thereafter the planet becomes dimmer.
Dec. 18-21: The waning crescent moon moves past the planets in our morning sky, brightening each in turn. The moon is nearest Mars on the 18th, Saturn on the morning of the 20th, and Jupiter on the 21st. Look in the east from about 4 a.m. on. Note that the moon moves, from day to day, along a line that is nearly parallel to the line between Mars, Saturn, and Jupiter. Observe how differently the planets themselves are arranged, relative to one another and to the nearby bright star Spica. They too (the planets) are moving, of course, in orbits that follow approximately the ecliptic (the plane of the earth's orbit), as does the moon.
Dec. 21: The sun arrives at the winter solstice at 5:51 p.m., Eastern standard time, and winter begins in the Northern Hemisphere. This is the shortest day of the year, in the sense that the sun is above the horizon for the shortest duration. The earliest sunset, however, occurs about Dec. 9 and the latest sunrise about Jan. 4. Midday, that is, the moment when the sun is highest , occurs midway between sunrise and sunset, of course.
Dec. 21-22: The Ursid meteor shower (about 15 per hour) reaches maximum after midnight. Not very spectacular, but with new moon on the 26th, the sky should be dark.
Dec. 28: Venus is just above the crescent moon tonight. On the 30th the planet begins its retrograde (westerly) motion, bringing it rapidly toward the sun.