Today is the 23rd of September 2018. Today’s length of the day and night are equal. It is called an Equinox. An equinox is a moment in which the plane of the earth’s equator passes through the center of the sun’s disk. It occurs twice in a year, 23rd September and 21 March.23th September equinox are called autumnal equinox and 21 march is called vernal equinox. On an equinox the length of day and night are approximately equal all over the planet.