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The Sun’s Rotation Period

In all human cultures the Sun has played a major role, and was thus observed by astronomers since ancient times. Sunspots (dark spots on the Sun's surface) were already reported more than 2,000 years ago by Chinese and Greek scientists. Since the 17th century, astronomers have tracked the motion sunspots across the solar disc, using these observations to measure the rotational speed of the Sun at different locations on its surface.

These observations led to the discovery that the Sun's rotation speed varies with latitude. This is due to the fact that the Sun is not a solid body. Because of its gaseous composition, the whole of it does not rotate at the same speed. This is what we call "differential rotation".


In this laboratory, students study the Sun's rotation by tracking sunspots in time-separated images taken with the CESAR solar telescope. By taking pictures every week, students can also participate in the world-wide campaign of sunspot tracking.

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