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Treebeard's Stumper Answer
5 Dec 97

Pretty Planets all in a Row

This week and next, weather permitting, we have a rare view of all the planets lined up in an arc across the southern sky just after dark. Don't miss it! Mercury is low in the southwest just after sunset. Above and to the left are reddish Mars and bright Venus. Jupiter is the bright star high in the south, and Saturn is in the southeast. You can't see Neptune, Uranus, and Pluto without help, but they are also in the sky, along with the crescent Moon. It's surprising that all the planets are in the sky at once, but it's not surprising that they are all in a line. Why?

It's not surprising that the planets are all in a line because the Solar System is nearly flat. The planets can be anywhere in their orbits around the Sun, but we only see them in the flat plane of the Solar System, along a slice of the sky called the ecliptic. As the planets orbit the sun, we see them slowly move back and forth along this path. Keep an eye on Venus and Mars over the coming week. They will approach closer and closer until they are only one degree apart, about the width of two full moons, on the night of the Winter Solstice on December 21!

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