Celestial Lights
By Phyllis Pitluga Dec 1, 2006

Closest grouping of three visible planets until 2050

For early risers between Saturday, December 9, and Tuesday, December 12, the eastern sky will display a conjunction (gathering) of Mercury, Mars and Jupiter. The last time three non-telescopic planets gathered this close was in 1980, and the next time will be in 2050. Because the planets are all moving (Mercury the fastest), their relationships will change day by day. Of the three, Jupiter is the brightest, then Mercury and last, Mars. Mercury is the closest to us (remember, it just passed across the Sun on November 8), and both Jupiter and Mars are almost on the opposite side of the Sun from us. 

This grouping is low in the southeast at the beginning of morning twilight. Look between 6:25 and 6:35am for the three to be just above the horizon (thus, you need to view toward a low or distant eastern horizon). Binoculars will help you find the planets more quickly at first but aren’t necessary for viewing. The event is non-telescopic, but if you have a telescope, you will enjoy viewing the planets themselves, apart from the grouping. Jupiter is by far the biggest and will also be accompanied by its four bright moons. Mercury is next in size and will appear as a tiny, nearly round world. Mars will be reddish and round in your telescope. Gatherings of the moving planets have inspired cultures throughout the world to view them with awe. 

Geminid meteor shower 

On December 13–14, Wednesday evening into Thursday by 2am, “shooting stars” will be festooning our holiday sky. The radiant of the shower rises at 7pm and is nearly overhead as the Moon rises at 2am. Thus, the best time is between 10pm and midnight when the shower radiant is comfortably halfway up in the eastern sky and the sky is still dark. Let your eyes adapt to the darkness of night and you will see ever-fainter stars and meteors. Under ideal sky conditions, you can see 120 meteors an hour—two a minute. For meteor showers you do not need binoculars or telescopes—just observe with your eyes.

These meteor shower particles are rocky grains associated with asteroid 3200 Phaethon. Every mid-December, the Earth orbits through this debris field.

The grains heat up from friction with Earth’s upper atmosphere, creating the glowing trails across our sky. These grains burn up and do not reach the surface of the Earth. So settle back in a chaise and let the “shooting stars” be your holiday celestial lights.

Winter solstice

Winter officially arrives on Thursday, December 21. The winter solstice is the time when the Sun rises farthest to the southeast, crosses lowest in the south at local noon and sets farthest to the southwest. This results in the fewest hours of daylight for the year, though here in the tropics we have almost 11 hours of daylight. In San Miguel, local noon is at 12:41pm. With the midday Sun halfway up in the south, noontime shadows are the longest for the year. Stand with your back to the Sun to see how long your shadow is on the winter solstice. 

Sky Calendar December 2006 

By following the Moon as the biggest and brightest “pointer” in the sky, during the month you can identify different planets and bright stars. On following nights you can relocate them but without the Moon—the Moon moves about 25 times its own diameter from one night to the next. The Moon is much closer than the planets of our Solar System, and the stars are even farther. So, when the Moon appears close to a celestial light they are truly separated by millions, billions or trillions of miles.

Pleiades Star Cluster

Dec. 3, Sunday: the Moon passes just above the Pleiades Star Cluster. 

Dec. 4, Monday: the Full Moon rises at sunset; for the next two weeks the Moon rises about 50 minutes later each night, making it also visible in the morning sky as the Moon orbits toward the direction of the Sun. 

Dec. 9, Saturday: Mercury passes two moon-diameters above Mars.

Dec. 10, Sunday: the Moon passes two moon-diameters above Saturn; Mercury passes just above Jupiter.

Dec. 11, Monday: Mars passes just below Jupiter.

Dec. 12, Tuesday: the Last Quarter Moon rises after midnight.

Dec. 13, Wednesday: the Geminid meteors peak.

Dec. 18, Monday: the waning Crescent Moon passes near Mars and Jupiter.

Dec. 20, Wednesday: New Moon (= no Moon because the dark side faces Earth). 

Dec. 21, Thursday: Winter solstice.

Dec. 27, Wednesday: First Quarter Moon, at sunset, is halfway across the sky from west to east and will continue orbiting eastward each evening.

Dec. 31, Sunday: the waxing Gibbous Moon passes just above the Pleiades Star Cluster to celebrate the New Year.

Phyllis Burton Pitluga is Astronomer Emerita of the Adler Planetarium and Astronomy Museum, Chicago, and is now a San Miguel resident.