February 29, also known as leap day or leap year day, is a date added to most years that are divisible by 4, such as 2008, 2012, 2016, 2020, and 2024. More details...

First Day of Fall. September equinox marks the moment the Sun crosses the celestial equator - the imaginary line in the sky above the Earth's equator - from north to south. On the equinox, night and day are nearly exactly the same length - 12 hours - all over the world.