Equinox

An equinox is commonly regarded as the moment when the plane of Earth's equator passes through the center of the Sun's disk, which occurs twice each year, around 20 March and 23 September. In other words, it is the point in which the center of the visible sun is directly over the equator. This simplified, but incorrect, understanding of Earth's orbital motion can lead to errors of up to 69 seconds from the actual time of equinox.