November 26, 2011

What's Up in December: Five major planets will put on show


The winter solstice will arrive at exactly 12:30 a.m. Dec. 22. This marks the longest night of the year for us in the Northern Hemisphere as the sun reaches its lowest point in our sky. There are several interesting highlights in December if you can brave the cold weather.

click image to enlarge

This chart represents the sky as it appears over Maine during December. The stars are shown as they appear at 9:30 p.m. early in the month, at 8:30 p.m. at midmonth and at 7:30 p.m. at month's end. Jupiter is shown in its midmonth position. To use the map, hold it vertically and turn it so that the direction you re facing is at the bottom.

Sky chart prepared by George Ayers

All five of the brightest planets will be well placed in the morning or evening sky, the Geminid meteor shower will peak the morning of Dec. 14, and there will even be a penumbral lunar eclipse.

Brilliant Venus will double its height in our evening sky, beginning the month at just 9 degrees above the western horizon 45 minutes after sunset and ending up at 18 degrees high at the same time by the end of the year.

It will be getting slightly less full even as it is getting closer and larger, so its actual brightness will remain at minus 3.9 magnitude all month. Look for our sister planet near the slender crescent moon in Capricornus the evening after Christmas, Dec. 26.

Jupiter will already be high in our southeastern sky as it gets dark enough to become visible. It will end its retrograde or westward motion Dec. 26. The King of the Planets was at its best at the end of October, but it is only slowly getting smaller and dimmer over the course of December. Watch as it passes close to the nearly full moon Dec. 6 and then watch the moon continue as it gets closer to full and passes just under the Pleiades on Dec. 8.

There was a very similar conjunction with the moon and Jupiter last month on Nov. 8. I was fortunate enough to watch and photograph that potentially dangerous asteroid, 2005 YU55, for nearly five hours that night.

Because it was moving so fast, about 30,000 mph, which translated to a full degree of the sky in under 10 minutes at that distance of 200,000 miles, less than the distance to our moon, it took us three hours of detailed and persistent work to even find it in the 16-inch Meade telescope at our Starfield Observatory in Kennebunk.

We finally found it right around midnight just as it entered the Great Square in Pegasus. It was quite faint at 11.2 magnitude, 100 times fainter than what the naked eye can see. It was only a quarter of a mile across, or about the size of an aircraft carrier, but that still qualified it as the largest asteroid that ever came that close to us.

It has been calculated that it will be no danger to Earth for at least the next 100 years, but since it does cross over our orbit, it could hit us at some time in the more distant future. Hopefully, we will have developed a way to safely deflect any such asteroid by then.

As this large chunk of rock tumbled through space, I tried to imagine what it would be like to walk on its dark and ominous carbonaceous surface, rich in metals and other valuable elements. This asteroid was knocked out of its safe orbit in the asteroid belt several thousand years ago, where it shared space with millions of similar rocks.

Looking down at our spaceship Earth from that height would give you a real sense of our home as perhaps the only living planet in the known universe. Although it is unlikely that we are the only planet with intelligent life, since we have already found more than 700 planets in other solar systems, if it did turn out that way in the future, it would make life on Earth even more precious.

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