What temporary feature did astronomers track to determine the Sun's rotation speed?

Answer

sunspots

Determining the rotation of the Sun presented a unique challenge because, unlike Earth, it lacks fixed, permanent topographical features such as continents or oceans that would serve as reliable markers. Early astronomers relied on tracking temporary but visible features on the solar surface, primarily dark, cooler regions known as sunspots. By noting the position of a distinct sunspot as it appeared to cross the solar disk and then observing its reappearance after traversing the unseen side of the Sun, scientists could accurately measure the time required for the body to complete a rotation. This method effectively utilized the sunspot as a transient, visible marker or clock hand attached to the surface of the plasma sphere, providing the necessary reference points for calculating rotational periods.

Related Questions

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sun astronomy rotation observation methods solar physics