Today marks the September equinox – the FirstDayOfFall in the Northern Hemisphere and the first day of spring in the Southern Hemisphere – which occurs when both hemispheres see equal amounts of daylight: How do you mark the changing seasons?
Complemented by cooler temperatures and falling leaves, the September equinox marks the beginning of the fall season for the Northern Hemisphere. This year’s autumnal equinox or spring equinox occurs on Sept. 22 at 8:04 p.m. CDT.
During an equinox the Sun shines directly over the equator resulting in nearly equal amounts of day and night throughout the world – except for the North and South Pole where the Sun approximately straddles the horizon for the entire day, according to Alphonse Sterling, an astrophysicist at NASA’s Marshall Space Flight Center in Huntsville, Alabama.
A visual aid to better understand how the Earth’s tilted axis causes the different seasons throughout the year in the Northern and Southern Hemispheres. Credit: NASA/Space Place