Rare planetary alignment in December

The feature on Sacred Monuments will be shelved this month to report on an extremely rare planetary occurrence reported by Roger Sinnot in this month’s issue of Sky & Telescope. For three days, beginning on the 10th and ending on the 13th, all of the planets, Mercury through Pluto, are arranged in their natural order outward from the sun in the Earth’s sky. However, only the planets Venus through Neptune will actually be visible on these nights. Sinnot says that the planets have not been in their proper order westward from the sun from before the invention of the telescope and it will not happen again for another four centuries. A proper alignment east from the sun last occurred in 1801 and will take place again in 2333.

Focus on the planets

Mercury is lost in the sun’s glare, reappearing near the end of the month. Look for Mercury on the 27th of the month, when it lies very near and just to the upper left of Venus, in the southeast about an hour before sunrise.

Venus rises in the southeast about two hours before the sun. Its brilliant presence cannot be mistaken for any other heavenly body.

Mars shares the southeastern horizon with its much brighter neighbor Venus. Look for Mars on two dates this month. On Dec. 9, it appears sandwiched between the crescent moon and Venus an hour before sunrise and then on the 20th, Mercury, Venus, and Mars form an ascending diagonal line on the horizon.

Jupiter appears above the eastern horizon around 2 a.m. as December opens but is not high enough on the horizon to afford good viewing until nearly dawn, where it is located among the stars of Virgo. Planet watchers with a telescope want to be on hand around 4 a.m. on Dec. 7 when the moon passes in front of, or occults, Jupiter. The planet reappears about an hour later.

Saturn rises in the east around 8 p.m. as December opens earlier each night thereafter. On Dec. 26, the full moon hangs directly above Saturn. The two bright stars to the planet’s upper left are Castor and Pollux.

Uranus and Neptune are low in the southwest at dusk where planet hunters will need binoculars and a finder’s chart. See the April issue of Sky & Telescope to spot them.

Pluto is lost to view in December.

December events

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

5 Moon in last quarter, 7:54 p.m. Brilliant Venus and much fainter Mars are very close in the predawn southeastern sky.

7 Don’t forget the occultation of Jupiter by the moon around 4 a.m. today.

9 Look to the southeast about an hour before dawn where Mars can be seen sandwiched between Venus and the crescent moon. Jupiter is high to the trio’s upper right.

12 New moon, 8:28 p.m. The moon is also at perigee, or closest approach to the Earth today, a combination of events that can lead to abnormally high or low tides.

13 The Geminid meteor shower peaks tonight and, with essentially no moon to interfere, this should be a great year for this major shower. Viewers can expect one to two fast-moving meteors per minutes radiating from the constellation of Gemini.

17 The sun enters Sagittarius on the ecliptic.

18 Moon in first quarter, 11:39 a.m.

20 Locate Venus on the southeast horizon about an hour before sunrise. The only hard part of this task will be getting out of a warm bed on a cold mid-December morning! Mercury is just to the lower left of Venus while Mars is to the upper right.

21 Winter solstice, 7:40 a.m. This represents the sun’s furthermost point in its journey south of the celestial equator making it the first day of winter, and the shortest day of the year, in the northern hemisphere. The reverse is the case in the southern hemisphere. The sun enters the astrological sign of Capricornus at the solstice but, astronomically, has just entered Sagittarius.

25 If you are outside watching for Kris Kringle on Christmas morning, look to the southeast, where Mercury and Venus are close together with Mars to their upper right.

26 Full moon, 10:06 a.m. The full moon is called the Long Night Moon because, from the northern hemisphere, it remains in view longer than at any other time during the year. It is also known as the Moon Before Yule as it is closest to the solstice.

27 The moon is at apogee or furthest distance from the Earth today. At dawn today, Venus and Mercury are close together with Antares to their immediate right. Mars is well to the upper right. Note that Saturn is directly below the moon around 7 p.m.

31 Sunrise, 7:13 a.m.; sunset, 4:04 p.m.

Clair Wood taught physics and chemistry for more than a decade at Eastern Maine Technical College in Bangor.