Astro Basics – Part 1

Astronomy, the Earth’s Rotation and the Seasons

All of the stars and planets in the night sky appear to move as the night progresses, but they don’t. In fact, this apparent movement is due to the rotation of the earth on its axis – the same rotation that causes the sun to move in the daytime sky. Over the course of one hour the earth rotates 15 degrees on its axis, and so the stars appear to move 15 degrees. For comparison, the full moon occupies about ½ a degree.

So the stars and planets rise in the East, and set in the West. They all rotate in an anti-clockwise direction about a point known as the celestial pole – an imaginary point directly above the earth’s north pole. For those of us in the Northern hemisphere, there is a star which happens to be almost exactly at this point. Polaris or the Pole Star is in Ursa Minor – the Little Bear – and all other objects appear to rotate around this one.

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