Monday, October 12, 2009

Big Dipper

The Big Dipper- a star group appeared in the sky in early March, 10.30 p.m., but by 3.30 a.m. It’s moved far to the west. The stars don’t really move, of course, but the earth is constantly on the go. Imagine the sky as the inside of a great hollow sphere, with the stars as fixed points on the sphere. Picture the earth as the center of that sphere.
Where you are on the earth and how the earth is moving determines which parts of the inside of the sphere you see. As the Earth revolves on its axis, the stars and constellations appear to revolve in the sky around a point directly over the axis. The earth not only revolves on its axis, but it also changes position as it orbits the Sun.
So in late September the Big Dipper will appear low in the sky. And in March of next year, it will appear to be in the same place it was this march.

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