September equinox 2025: All you need to know

Facebook Tweet PinShares

The September equinox is the time of year when the sun appears to cross the celestial equator—an imaginary line in the sky directly above Earth’s equator—from north to south.

September equinox 2025

Satellite view of Earth during equinoxes and solstices. On the September equinox, the terminator – the line between light and dark – moves from pole to pole because the sun sits directly above the equator. (Image credit: NASA’s Earth Observatory)

When it occurs: The September equinox will fall on September 22, 2025, at 18:20 UTC (2:20 p.m. EDT).

Effect on day and night: As the sun will appear directly above Earth’s equator on September 22, 2025, Earth’s two hemispheres will receive equal amounts of sunlight. In other words, day and night will be nearly equal in length for everyone across the globe – about 12 hours.

After the September equinox, the sun moves southward as seen from Earth. As a result, people living in the northern hemisphere receive less sunlight – the days are shorter and the nights are longer and people living in the southern hemisphere receive more sunlight – the days are longer and the nights are shorter.

Effect on season: The September equinox on September 22, 2025, marks the beginning of autumn (autumnal equinox) in the northern hemisphere and the beginning of spring (vernal equinox) in the southern hemisphere.

Effect on sunrise and sunset: As the sun crosses the celestial equator on the equinoxes, the path of the sun across the sky – the ecliptic – intersects the celestial equator on the equinoxes.

The ecliptic and the celestial equator intersect on the equinoxes. (Image credit: NASA)

Now, the celestial equator intersects your horizon at points due east and due west, no matter where you are on the globe. So the sun will rise exactly to the east and set due west on September 22, 2025.

After the September equinox, the sun rises and sets a bit farther south on the horizon each day until the December solstice (see the image below).

Zaid M. Al-Abbadi captured the sunrise direction each month in 2019 from near the city of Amman, Jordan. The sun rises due east on the equinoxes. However, it rises furthest to the north of east on the June solstice and furthest south of east on the December solstice. (Image credit: Zaid M. Al-Abbadi/APOD)

Why do equinoxes occur?

The equinoxes and solstices occur due to Earth's tilt on its axis as it orbits the sun — The equinoxes and solstices occur due to Earth’s tilt on its axis as it orbits the sun. (Image credit: NOAA)

Earth’s rotational axis is tilted about 23.5° from the perpendicular with respect to its orbital plane around the sun.

As a result, the amount that Earth’s axis tilts towards or away from the sun varies throughout the year.

Twice a year, in March and September, Earth’s axis is tilted neither towards nor away from the sun. In fact, the axis is then perpendicular to the sun, resulting in a nearly equal length of day and night across the globe. These instances are referred to as equinoxes.

The word “equinox” comes from two Latin words: aequus (equal) and nox (night).

Please bookmark Spaceandtelescope.com or follow us on Facebook and Twitter to get latest space news, upcoming skywatching events and astronomy-related content.