The first day of fall in 2025 is September 22nd. The autumnal equinox, which marks the official start of fall in the Northern Hemisphere, occurs when the sun crosses the celestial equator moving southward. During the autumnal equinox, the day and night are of equal length all over the world.
The changing of the seasons is caused by the Earth’s tilt on its axis as it orbits the sun. As the Earth orbits the sun, different parts of the planet are tilted towards or away from the sun. This tilt causes the amount of daylight to vary throughout the year, resulting in the seasons.
