First Day of Fall

Celebrated on 09/22/2026

Quick Fact

The First Day of Fall, also known as the autumnal equinox, occurs when the Sun crosses the celestial equator heading south, resulting in nearly equal day and night worldwide. In 2024, it falls on September 22 at 12:44 UTC. This astronomical event marks the official start of autumn in the Northern Hemisphere.

Origins and Establishment of First Day of Fall

The First Day of Fall, or autumnal equinox, has been recognized by civilizations for millennia. Ancient cultures like the Maya, Greeks, and Chinese celebrated the equinox as a time of harvest and balance. In modern times, the astronomical definition was standardized by the International Astronomical Union in the 20th century, establishing the equinox as the precise moment when the Sun's apparent geocentric longitude is 180 degrees. This scientific precision replaced earlier folk calendars that relied on fixed dates.

Evolution and Modern Commemoration

Today, the First Day of Fall is celebrated globally with festivals like the Chinese Mid-Autumn Festival, the Jewish Sukkot, and various harvest festivals. In the United States, it is often associated with pumpkin spice, apple picking, and fall foliage. While not a public holiday, many schools and businesses acknowledge it with seasonal activities. The equinox also serves as a reminder of Earth's axial tilt and its role in seasonal changes.

Facts & General Observations

• The autumnal equinox is one of two times per year when the Sun rises exactly due east and sets exactly due west.
• In the Northern Hemisphere, the autumnal equinox marks the start of a 6-month period of decreasing daylight until the winter solstice.
• The word "equinox" comes from Latin "aequus" (equal) and "nox" (night), but day and night are not exactly equal due to atmospheric refraction and the Sun's disk size.

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