Precession, the Earth’s ‘wobble’ on its axis of spin as it orbits the sun, accounts for the fact that it enters different astrological and astronomical constellations each month. Precession also explains two other celestial phenomena, one being that the pole star shifts over time and the other the definition of a celestial age. About 4,000 B.C., the pole star was Thuban in Draco and the Egyptians built the Great Pyramid to note the direction of north. Today, the pole star is Polaris in the Little Dipper and, by 14,000 A.D. will have shifted to Vega in Lyre. An age is defined by the constellation that the sun is in at the vernal equinox. Millennia ago, it was the Age of Taurus followed by the Age of Aries. Today we are in the Age of Pisces, while many look forward to the upcoming Age of Aquarius. Because constellations cover such vast expanses of the sky, there is a great deal of controversy over when the Age of Aquarius will arrive.

Focus on the planets

All planetary action favors early risers this month as Jupiter, Mars, Venus and Saturn are all in the late night and predawn sky.

Mercury remains hidden until midmonth, when it hovers above the southwest horizon about 15 minutes after sunset. By month’s end, Mercury does not set until about an hour and a half after sunset.

Venus is conspicuous in the southeast by 4:00 a.m., though it is starting to lose a bit of its luster. Venus is occulted by the moon on Dec. 7, but unfortunately, this takes place during the daytime hours.

Mars rises in the east about 2:00 a.m. but appears as little more than a reddish-orange dot by telescope.

Jupiter rises in the west shortly after midnight as December opens but two hours earlier by month’s end. The planet’s belts and zones will be readily observable as are the antics of its four major moons about and across the face of the planet.

Saturn becomes visible at midmonth, when it rises in the southeast about an hour before sunup and two hours before sunup at month’s end. Watch Venus and Saturn draw closer together as December closes with a close conjunction taking place on Jan. 9.

Uranus rises in the southeast among in Pisces where its blue-green disk should be available by binoculars.

Neptune is high in the southwest as darkness falls where its blue-gray disk may be found among the stars of Aquarius. It sets about 10:00 p.m. and will prove reasonably easy to spot with binoculars. Sky and Telescope magazine provides a finder’s chart for the two outermost planets at skypub.com/urnep.

December events

1 Sunrise, 6:52 a.m.; sunset, 3:56 p.m.

3 Moon in last quarter, 2:40 a.m. Note Jupiter directly to the left of the moon about an hour before sunrise.

5 The moon is at apogee or farthest distance from the Earth. Mars is to the lower left of the moon an hour before sunrise.

7 The moon is extremely close to Venus before dawn with occultation taking place during the daylight hours.

11 New moon, 5:29 a.m.

14 Geminid meteor shower peaks tonight but should last over the next few days. The recent new moon will pose little problem for viewers who can expect up to a maximum of 120 meteors per hour emanating from a point near Castor of Gemini.

18 First quarter moon, 10:14 a.m. The sun enters Sagittarius on the ecliptic.

21 Moon at perigee or closest approach to Earth. Winter solstice,11:48 p.m. in the northern hemisphere. The sun enters the astrological sign of Capricorn at the solstice.

25 Merry Christmas! Celebrate by observing the full moon at 6:11 a.m. The full moon of December is known as the Long Night Moon.

31 Venus is in the southeast about 45 minutes before sunrise with Saturn to its lower left. Later, about 6:00 a.m., Jupiter is to the upper left of the moon in the southwest. Sunrise, 7:13 a.m.; sunset, 4:04 p.m.

Send astronomical queries to Clair Wood at cgmewood@aol.com or care of the Bangor Daily News, Features Desk, P.O. Box 1329, Bangor, ME 04402.