Focus on the planets

Mercury will be hidden in the sun until the last few nights of the month, when it briefly appears at twilight for a good showing during the first half of January.

Venus has been slipping steadily into the morning twilight all fall and will disappear early in December.

Mars glows with a reddish-orange hue high on the southern horizon at dusk. Look for Fomalhaut below, and slightly to the left of the red planet.

Jupiter appears on the east-northeast horizon shortly after dark as the month opens. By December’s close, the giant planet will be visible at twilight.

Saturn is low in the east at twilight but climbs steadily all night. Look for orange-colored Aldebaran to Saturn’s immediate lower right. In the pre-dawn hours of Dec. 28, the moon will pass in front of Saturn, an event visible in all of North America. This will take place at approximately 4 a.m.

Uranus is in eastern Capricornus just to the lower right of Mars, where its greenish disk should be visible through binoculars.

Neptune is also in Capricornus but will be difficult to spot because of it is visible only at twilight.

Pluto is lost to view during December.

Our celestial neighborhood

Neptune, the eighth planet of the solar system, lies nearly 30 times farther from the sun than does Earth. Its year is more than 165 Earth years.

Neptune was discovered because it perturbs the orbit of Uranus, which was spotted in 1781. In 1846, a French mathematician named Leverrier calculated Neptune’s position from the discrepancies in the orbit of Uranus and told astronomers where to look. It was discovered the same night the search began!

One of Neptune’s eight moons, Triton, is actually of more interest than the planet itself. Pictures taken by Voyager 2 in 1989 showed that Triton has active volcanoes spewing crystals of frozen methane. There are also features that appear to be frozen lakes of methane, ammonia, and water. Triton, at -400 degrees Fahrenheit, is the coldest known region of the solar system.

December events

1 Sunrise, 6:52 a.m.; sunset, 3:56 p.m. The moon is midway between Saturn and Jupiter tonight.

2 Jupiter is slightly below the moon tonight, with Betelgeuse to the moon’s right.

6 Moon at perigee, or closest approach to Earth, tonight.

7 Moon in last quarter, 2:53 p.m.

14 New Moon, 3:48 p.m. If you missed the Leonid meteor shower last month, all is not lost, for the Geminid meteor shower peaks tonight. There is no moon to interfere so, after about 10 p.m., look for one or two “shooting stars” every minute.

18 The sun enters Sagittarius on the ecliptic.

20 Look for Mars to the moon’s upper right early in the evening. The solitary star to the lower left of the red planet is Fomalhaut.

21 The winter solstice occurs at 2:20 p.m. The sun is farthest south for the year, marking the start of winter in the northern hemisphere. The sun is also entering the astrological sign of Capricornus but, astronomically, has just entered Sagittarius. The moon is at apogee, or farthest distance from the Earth, tonight.

22 Moon in first quarter, 3:57 p.m.

25 Merry Christmas!

27 The moon, Saturn, and Aldebaran make up a tight triangle tonight.

30 Full Moon, 5:41 a.m. The full moon of December is called the Long Night Moon or the Moon After Yule.

31 On your way home from your New Year’s Eve celebration, pause and look to the south, where brilliant Sirius, the Dog Star, greets you well up on the horizon. Higher, and directly above Sirius, is Jupiter, with Saturn and Aldebaran to its right. Sunrise, 7:13 a.m.; sunset, 4:04 p.m. Happy New Year!