Is the day and night exactly 12 hours on an equinox?
Quick Answer: No, day and night are not exactly 12 hours each on an equinox. The day is slightly longer than the night due to atmospheric refraction and the sun’s apparent size.
On an equinox, the sun crosses the celestial equator, making day and night close to equal. However, the atmosphere bends sunlight, allowing us to see the sun before it actually rises and after it sets.
Also, the sun isn’t a point but a disk, so sunrise and sunset span a few minutes. Both factors make the daytime a bit longer than 12 hours on the equinox.