Why does Autumn begin?

The leaves may not have changed color yet and you may not feel much cooler weather but autumn is about to begin in the Northern Hemisphere.

Every year, around September 21 to 24, the September Equinox marks the beginning of autumn in the Northern Hemisphere and spring in the Southern Hemisphere.

What is the September Equinox?

An equinox happens when the Sun crosses the Earth’s equator as it appears to move from one hemisphere to the other. During the September Equinox the Sun rises almost directly in the east and sets almost directly in the west.

Day and night are also nearly equal in length at about 12 hours each.

Why do seasons change?

Earth is tilted about 23.5 degrees as it travels around the Sun. This tilt is the main reason we have different seasons.

At different times of the year one hemisphere receives more direct sunlight while the other receives less.  During the equinoxes neither hemisphere is tilted strongly toward or away from the Sun.

When is the Equinox?

The September Equinox occurs around September 22 or 23, depending on the year and location.  The next major equinox is the March Equinox which marks the beginning of spring in the Northern Hemisphere.

In 2026, the March Equinox will occur on March 20.

Equinox vs. Solstice

Equinoxes are different from solstices. During an equinox day and night are nearly equal.  A solstice marks the year’s longest or shortest day.

In the Northern Hemisphere the December Solstice brings the shortest day and longest night of the year.

In 2026, it will occur on December 21.

A Fascinating Fact

The Sun appears to move across the horizon very quickly around the equinox.  Sunrise and sunset can seem especially rapid because the Sun’s path is more closely aligned with the horizon at these times.

The equinox is therefore more than just a change in the calendar it is a reminder of how Earth’s tilt and movement around the Sun shape the seasons we experience.