Eclipses of the sun occur when the moon passes between the earth and sun. They can only occur at the time of new moon. There must be at least two solar eclipses every year separated by an interval of six months and there may be as many as five solar eclipses in a year. Eclipses of the moon occur when the earth comes between the sun and moon, and the moon passes into the earth's shadow. Eclipses of the moon can only occur at full moon. There may or may not be eclipses of the moon every year. The greatest number of eclipses than can occur in any one year, solar and lunar combined, is seven and the least number is two and in that case they are both solar eclipses.