December Sky Chart
Dec. 1: The moon was full on Tuesday, and tonight's gibbous moon is in Taurus , rising soon after sundown, moving between El Nath (above) and Zeta Tauri (to the right), the stars that mark the ''horns'' of the Bull.
Dec. 2: Perigee moon (nearest earth) occurs this morning, and will ''stretch out'' the higher spring tides that followed the full moon. Expect continuing higher tides tonight and tomorrow.
Dec. 3: The waning gibbous moon rises several hours after sunset in line with and below the ''Twin'' stars Pollux and Castor in Gemini.
Dec. 5-6: Shortly after moonrise (about 10 p.m.), look for Regulus, the bright star of Leo, below and to the moon's left. The moon moves east (left) past Regulus during the night as both drift westward across the sky.
Dec. 7: Last quarter moon, rising about midnight near the autumnal equinox, where the sun is when fall begins each September. The bright star above the moon is Denebola, at the ''tail'' of Leo, the Lion.
Dec. 8: The earliest sunset of the year occurs today, the latest sunrise on Jan. 6.
Dec. 10: The waning crescent moon rises before dawn near Spica (the bright star of Virgo) and Saturn.
Dec. 11: The waning crescent moon may still be visible in the east just before and during morning twilight. Look early, and you may also see two second magnitude stars nearby, Zubenelgenubi to the moon's right and Zubeneschamali above. These are the two brightest stars of the constellation Libra.
Dec. 13: Jupiter and the moon are in conjunction, but they rise in the morning twilight too late to be seen.
Dec. 14: The Geminid meteor shower, second only to the Perseids of August in reliability and production, is at maximum. You may see up to 50 meteors per hour after midnight of the 14th and 15th.
Dec. 15: New moon is in Sagittarius, near the winter solstice. A partial solar eclipse occurs today, not visible in the Americas.
Dec. 17: The apogee moon (farthest from earth) may be visible as a slim crescent in evening twilight, at the western edge of Capricornus.
Dec. 18: Look for the crescent moon in the southwest at dusk, and you should see it pass from right to left below Mars, closest to the planet about 8 p.m. Eastern standard time.
Dec. 21: At 11:39 p.m., EST, the sun is 90 degrees (6 hours) west of the vernal equinox and 231/2 degrees south of the equatorial plane, a point in the constellation Gemini called the winter solstice. This marks the beginning of winter in the Northern Hemisphere. Note that it is not the date of the earliest sunset or of the latest sunrise (see above), although it is the ''shortest'' day of the year as measured by the total interval during which the sun is above the horizon.
Dec. 22: Maximum of the Ursid (from Ursa Major, the Great Bear) meteor shower is at 1400 EST. You may see up to 15 shower meteors per hour during the dark, moonless morning hours today and tomorrow.
Dec. 23: Setting at midnight in the constellation Pisces, almost exactly at the vernal equinox, the moon is at first quarter.
Dec. 27: The fuzzy-looking group of dim stars to the right and above the moon is the Pleiades (Seven Sisters) in Taurus. The moon moves left away from them and closer to Taurus's brightest star, Aldebaran, during the night, passing above Aldebaran during the day on Tuesday.
Dec. 30: Full moon occurs at about 6:33 a.m., EST, in Gemini, and a total lunar eclipse is visible throughout North America (see box). Two bright stars to the east and above the moon are Pollux (the brighter) and Castor, the ''Twin'' stars. Perigee moon (nearest earth) also occurs today.
Dec. 30: Mercury is at maximum distance to the sun's left (greatest easterly elongation), best located for viewing as an evening star. It is low in the west-southwest in twilight. Venus is also there, much easier to see because of its brightness. With Venus in view, look for Mercury to its left. Their positions relative to each other and to the setting sun are about the same for several nights before and after the 30th.
Dec. 30-31: With perigee occurring only 101/2 hours after full moon on the 30 th, watch for exceptionally strong tides late Thursday and during the day on Friday, as the perigee effect adds to the full moon spring tide.
All month: We're hard pressed to find an impressive ''Christmas Star'' this year. Best we can do for an exceptional event is the total lunar eclipse of Christmas week. But don't overlook the winter sky itself! In the west, the early evening still features the three bright stars of the Summer Triangle, Altair, Deneb, and Vega. Deneb stands highest of the three, with the Northern Cross upright and easy to see beneath it, and the Milky Way slashing past it. The east , of course, contains the brightest stars of the year, those of Orion, Canis Major, Canis Minor, Gemini, Taurus, and Auriga, ranged along a great ''belt'' from south to north.