Measuring the size of the shadow of the Earth


A lunar eclipse occurs when the moon passes directly into the shadow of the earth. This can occur only when the sun, earth and moon are exactly, or very closely, aligned, and the earth is between the sun and the moon. Hence, a lunar eclipse can only occur on the night of a full moon.

11 November, 2015

In this activity you will learn how to measure the size of the shadow created by the earth on the lunar surface during a total lunar eclipse. To do this, the times of arrival and departure of the shadow as it passes over several lunar craters are measured. Alternatively, the curvature of the earth’s shadow against the moon can be used to determine the size of earth’s shadow. Both methods are described in this document.

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