All Is Bright for Jupiter, Venus

Unwrap a bounty of night-sky gifts this holiday season: visible planets, glorious conjunctions, a close-up full moon and a change of season.

Jupiter and Venus begin December in conjunction at dusk in the southwestern sky. If the sky remains clear, the Jupiter-Venus conjunction, officially occurring tomorrow night, will be spectacular. Venus is the brighter of the two planets, and it remains high in the southwest throughout December, while the gaseous Jupiter descends the western horizon all month.

Venus, ever effervescent, is visible at negative fourth magnitude (ultra bright), and it is easily mistaken for a distant jetliner approaching Dulles International Airport with its landing lights on. Jupiter at negative second magnitude is bright enough to enjoy from the urban light-polluted sky. At month's end, Venus sets after 8 p.m., and Jupiter sets before 6 p.m.

Tonight, notice that the sliver of a young moon is below Jupiter and Venus, while tomorrow night the crescent can be seen above the planetary duo. Young moons always appear briefly in the western sky at dusk and early evening.

At the very end of December, the fleet Mercury (zero magnitude, or bright) joins with Jupiter at dusk in the southwest for another conjunction. The brighter Jupiter is to Mercury's left, and Venus is far above the fray.

The full moon Dec. 12 will be at its closest (356,556 kilometers, or 221,554 miles) to Earth since 1993, and the full moon won't be this close again until 2016. Once a month the moon gets close to Earth at perigee, but sometimes the monthly lunar perigee coincides with the full moon. On Jan. 1, 2257, the full moon will be closer than this year's event -- at 356,371 kilometers, or 221,439 miles -- according to Belgian astronomer and mathematician Jean Meeus. Concerning this phenomenon, the radio program "Earth and Sky," by Deborah Byrd and Joel Block, provides excellent details on its Dec. 12 podcast, found at http://www.earthsky.org/skywatching. The podcast link is on the right side of the page.

Saturn, the beloved ringed planet, is a late night owl. It rises before 1 a.m. in the southeast now, while at the end of the month it rises about 11 p.m. Its rings are nearly edge-on, and the planet is found in the constellation Leo.

The official start to winter in the Northern Hemisphere -- the Winter Solstice -- occurs at 7:04 a.m. Eastern Time on Dec. 21, according to the U.S. Naval Observatory. Before long, our short days will start to get longer.

Down-to-Earth Events

· Tomorrow -- "The Stars Tonight" unveils the December night-sky action at Arlington County's David M. Brown Planetarium, 1426 N. Quincy St., adjacent to Washington-Lee High School. 7:30 p.m. $3 for adults, $2 for seniors and children. For details, call 703-228-6070.

· Tuesday -- Astronomer Max Mutchler, who discovered Pluto's moons Nix and Hydra from images

by the Hubble Space Telescope,