Are the stars out tonight?
Jupiter and Venus have been putting on quite a display in the twilight and evening skies, and the moon has been joining them. The show has been taking place in front of the constellation Sagittarius, which has very few really bright stars to take our attention away from the planets.
The closest Venus and Jupiter came to each other from our vantage point here on Earth was on Nov. 30 and Dec. 1, when they were only 2 degrees apart. Venus and Jupiter are the two brightest planets in our solar system, which makes them easy to spot. Their brightness comes from sunlight bouncing off their highly reflective, cloud-covered surface. Venus is the brightest of the two, and the closest to us at 94 million miles away. It is the second planet from the sun.
Jupiter, the largest planet and next- brightest planet in our solar system, is 540 million miles away and the fifth planet from the sun. But when we look out across the solar system at where those two planets happen to be in the course of their orbits, from our perspective they sometimes look like they are side by side. Sky watchers call such a close pairing a conjunction.
Venus and the crescent moon will be next to each other again on New Year's Eve. But they won't be near Jupiter by then. Things keep moving in the sky, especially Venus. Jupiter and Venus are in conjunction about once a year or so, but not necessarily in the night sky where we can see them.
The last time Venus and Jupiter could been seen this close to one another in the night sky was back in September 2005. Their next visible conjunction will be May 2011 in the morning and March 2012 in the evening. Neither of those conjunctions will position the two planets as close as they are right now. The next time they'll be that close or closer won't be until May, 2013.
If you have been keeping track of Jupiter and Venus you would have seen them gradually narrowing the distance between each other during November. Jupiter was on top, Venus was near the horizon. But as the days and weeks went by, Venus kept inching toward Jupiter until it came up alongside the giant gas planet and eventually passed it. Venus only takes 224.7 days to complete its orbit around the sun. Jupiter's orbit takes 11.86 years.
As long as you're outside checking out the planets and the moon, the full moon on Dec. 12, called the Long Nights Moon or the Full Cold Moon by American Indians, will be 221,554 miles away from the Earth, which is closer than it has been since 1993. You'll have to wait until Nov. 14, 2016 for a full moon to be this close again.
The Geminid meteor showers peak on Sunday, Dec. 14. Falling at the rate of 75 per hour, or a little more than one a minute, the meteors would be easy to spot were it not for that close, fat moon. The moon will be two days from its full phase when the Geminids are at their strongest. That means that the bright moonlight will wash out our view of some of the dimmer meteors in the December showers.
Moonlight isn't the only reason some of us see very little of what's happening in the night sky. Light pollution is much bigger factor. It's such a concern that the November 2008 issue of National Geographic magazine made "Our Vanishing Night" its cover story.
In the article, Verlyn Klinkenborg writes, "Nearly all of nighttime Europe is a nebula of light, as is most of the United States and all of Japan. In the south Atlantic the glow from a single fishing fleet — squid fishermen luring their prey with metal halide lamps — can be seen from space, burning brighter, in fact, than Buenos Aires or Rio de Janeiro."
In days of old, Klinkenborg notes, the night was dark enough for Venus to cast shadows on Earth.
In most over-lit urban settings today, only the brightest stars and planets can be seen. For those who live there, the delicate pearlescent Milky Way is something seen only in photographs. By contrast, the view in "Big Sky Country" Montana is so densely strewn with stars that it looks like you can reach up and touch them. In places like that it is difficult for people just learning to recognize the constellations to pick them out from among all the other stars filling the sky.
Klinkenborg asserts that we and the other species with whom we share the planet need the light of the stars and the rhythm of day and night. They are as much a part of our biology as they are of our heritage.
"In a very real sense," he wrote, "light pollution causes us to lose sight of our true place in the universe, to forget the scale of our being, which is best measured against the dimensions of a deep night with the Milky Way — the edge of our galaxy — arching overhead."
Then there's the winter solstice ...