equilux

Each of the two days of the year on which, at a given location, there are exactly 12 hours of light (with insolation) and 12 of darkness (without it). Due to the angular width of the solar disk (approximately 32' of arc), it does not coincide with the equinox, with the spring equilux occurring a few days before the equinox of the same name and the autumn one occurring a few days after. At the equinoxes, the length of day and night is equalized, but sunrise is considered to occur when the center point of its disk appears above the horizon, and sunset when that point sets below it.