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How to calculate sidereal time animation

Time on Earth is usually measured relative to the sun. It's called solar time.

One solar day takes 24 hours, defined by one full rotation of Earth around its north-south axis relative to the sun.

Time can also be measured relative to the stars many, many millions of kilometres from Earth. This is called sidereal time.

One sidereal day equals one full rotation of Earth around its north-south axis relative to distant stars. One rotation takes 23 hours, 56 minutes and 4 seconds.

The difference between solar and sidereal time increases by 3 minutes and 56 seconds each day. This is because Earth rotates not only around its north-south axis but also orbits around the sun.

Watch the sidereal time video

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