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The Sky This Week, 2010 December 14 - 21

A lunar eclipse, the Winter Solstice, and icy planet atmospheres heat up.

South Equatorial Belt Outbreak on Jupiter,
Imaged between 2010 NOV 29 and DEC 10

The Moon waxes to the Full phase this week, climbing to her highest declination to beam down on us from just above the "club" of Orion. Full Moon occurs on the 21st at 3:13 am Eastern Standard Time. December’s Full Moon is variously known as the Cold Moon, Long Night Moon, or Moon before Yule. This year it might be called the Vanishing Moon since Luna will undergo a total eclipse by the shadow of the Earth. The eclipse begins with the penumbral phases starting at 12:28 am EST on the 21st. Most of us won’t notice much change in Luna’s appearance until shortly before the Moon enters the umbral shadow at 1:32 am. The shadow slowly creeps across the Moon’s face, completely covering it at 2:40 am. Mid eclipse occurs at 3:17 am, then the total phase ends at 3:54 am. The partial eclipse continues until 5:02 am, when Luna exits the umbral shadow. The penumbral phases end at 6:06 am. During a total eclipse the Moon’s typical appearance is a dull red, but sometimes it can be a lighter coppery hue or so dark that it can’t be seen unless you know exactly where to look. These colors are telltale signs of the opacity of Earth’s upper atmosphere. With the recent eruption of Mt. Merapi in Indonesia this year’s eclipse might be especially dark. Only time will tell! If you’re looking for something lunar to observe before the eclipse, you can watch the Moon slide slowly south of the Pleiades star cluster on the night of the 18th.

The 21st also marks the beginning of the astronomical season of winter, with the Winter Solstice occurring at 6:38 pm on the 21st. This is the moment when the Sun reaches its southernmost declination in the sky and we experience the year’s shortest day in the Northern Hemisphere. At this time the Sun stands directly over the Tropic of Capricorn over the remote islands of Kiribati in the South Pacific Ocean. Gradually over the next few days, then more rapidly as the new year begins, Old Sol will climb back toward more northern climes. Spring is surely on the way!

Mercury’s brief flirtation with the evening sky is now over. The fleet planet will pass between the Earth and Sun on the 20th, then rapidly enter the morning sky to be well-placed for pre-dawn viewing by the end of the year.

Jupiter is once again the sole bright planet to grace the evening sky. Old Jove sits high in the south on the meridian as evening twilight wanes, dipping into the southwestern sky during the later evening hours. Jupiter has been putting on an especially good show for small telescope owners over the past several weeks. Since early November a small area of activity in the area of the once-prominent South Equatorial Belt has spread out to encircle most of the planet in what is regarded by most Jove-watchers as the first stage of the resurgence of the belt. There are still several weeks left in the jovian observing season, so it will be very interesting to watch the progress of this major atmospheric event on the solar system’s largest planet.

Not to be out-done, the planet Saturn, which now rises shortly before 2:00 am, has popped a surprise of its own in its atmosphere. Normally the ringed planet’s storms are harder to see than those on Jupiter because of a high-altitude methane "smog" that hides its banded clouds, but last week a bright white spot was discovered by amateur astronomers in the planet’s northern hemisphere. If his widening rings weren’t enticement enough, this feature is worth setting the alarm clock to see over the next few weeks.

Finally, bright Venus still dominates the view to the southeast as morning twilight gathers. The dazzling planet finishes out the year as a sentinel for the rising Sun, so if you’re up before dawn she’ll throw a little extra light into the longest of the year’s nights.