The night sky is a model of order and precision. The same stars wheel overhead at the same time each year. The Moon passes by the stars with clockwork regularity. And once you understand how the universe is arranged, even the bright "wanderers" -- the planets -- move along precise, predictable paths.
Consider the planets Venus and Jupiter -- the brightest pinpoints of light in the night sky. They line up quite low in the southeast at dawn tomorrow. Venus is the brighter one, with Jupiter below it.
Scientists puzzled over the motions of Venus, Jupiter, and the other planets for millennia. These bright bodies follow roughly the same path across the sky as the Sun. But they sometimes stop and reverse direction. In early concepts of the cosmos, where Earth was considered the center of the universe, these motions were hard to explain.
But it was these very motions that eventually helped scientists find the right order. If you place the Sun at the center of our solar system, with Earth and the other planets orbiting it, then everything makes sense. Some of the planets are closer to the Sun than Earth is -- like Venus. And some are farther -- like Jupiter.
Understanding the layout allows astronomers to predict the motions of the planets -- and to know when they'll pass by each other. Venus and Jupiter, for example, will meet up again in November -- this time in the evening sky.
More about Venus and Jupiter tomorrow.
Script by Damond Benningfield, Copyright 2007
For more skywatching tips, astronomy news, and much more, read StarDate magazine.
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