During an equinox, places around the globe experience nearly equal amounts of daytime and nighttime. The second occurrence this year happens on Sunday.

The official start to the fall season, the autumnal equinox, occurs on Sunday, Sept. 22. What exactly happens during the equinox? Here’s a breakdown: According to NOAA, an equinox occurs when the Earth’s axis is tilted neither away nor toward the sun.

However, KOIN 6 Meteorologist Kelley Bayern says that, due to several factors – such as latitude and location, as well as the bending of sunlight through our atmosphere – most locations in America don’t have exactly equal daylight and nighttime hours on the date of the fall equinox.