The difference between the times of moonrise on successive nights, due to the Moon’s motion in its orbit. It has an average value of 50.4 min, but the actual figure can vary widely depending on the Moon’s declination. On about September 23, the autumnal equinox, the full Moon rises only 18 min later on successive evenings. This is known as the harvest Moon. A similar effect in October is called the hunter’s Moon.