Why a lunar eclipse occurs during a full moon?
During a new moon, the moon is between the sun and the Earth. Thus, the Earth cannot cast its shadow on the moon. Recall that, during a full moon, the Earth is between the sun and the moon. In this position the Earth can block the light from the sun and cast its shadow on the moon. Therefore, a lunar eclipse can occur only during a full moon. However, an eclipse does not happen every month when there is a full moon. Why? As the moon revolves around the Earth, it may pass above or below the Earth’s shadow. In this way the earth’s shadow does not fall on it. Therefore, no eclipse happens. Astronomers can predict accurately the occurrences of eclipse. Each year there are at least two solar eclipses and three lunar eclipses that may be seen from different places on Earth.
