Understanding the Meaning of the Fall Equinox Date and Time

While some areas of the U.S. are already experiencing the change of the seasons, the official start of the astronomical fall is this weekend. Here are a few things to know about the start of the fall season, also known as the equinox or the beginning of autumn.

When Does Fall Officially Begin?

The official start to fall happens on Sunday, September 22. If you are located in the Eastern time zone, the season begins at 8:43 am. In the Central time zone, the formal beginning is at 7:43 am while the season kicks off at 6:43 am in the Mountain time zone and bright and early at 5:43 am in the Pacific time zone.

But why does the season officially start at this exact time? The answer lies with how the sun's rays shine on the equator. These rays shine down twice a year directly over the equator. The first time happens either on March 20 or 21 and the second time happens on either September 22 or 23. The March date is known as the spring, or vernal, equinox while the September date is known as the fall, or autumnal, equinox while in the Northern Hemisphere. The opposite is the case in the Southern Hemisphere.

The term "equinox" is a derivative of the Latin word "aequi," meaning equal, and the word nox," meaning night. Thus, together, the words translate to "equal night."

The specific time comes from when the sun's direct rays pass exactly over the equator from the Northern Hemisphere to the Southern Hemisphere. This specific time varies from year to year. However, you can count on the autumnal equinox always happening between September 21 and September 23. The astronomical fall ends on the date of the winter solstice, happening between the dates of December 20 and December 22. These dates change annually as the result of leap years and the natural elliptical shape of the Earth and its journey around the sun.

Although daylight and nighttime hours are balanced on the equinox, those in the Northern Hemisphere can expect the hours of light to decrease after the fall equinox. This is because of the natural tilt of the hemisphere away from the sun. When picturing this, it is important to remember that the axis of rotation of the Earth is perpendicular to the line that connects the two centers of the planet and the sun during any equinox. As a result, daylight and nighttime are balanced to almost 12 hours each across the world.

The daylight hours in the Northern Hemisphere will now grow shorter up until the winter solstice, scheduled on December 21 this year. It is the opposite situation in the Southern Hemisphere. In this area of the globe located to the south of the equator, the September equinox is the beginning of the spring season. This means that daylight will get longer until the start of the summer period in December.

Because of the variability in the dates of the equinox, it can be challenging for statisticians to track data from year to year. This is why most tracking databases use information from the meteorological season dates, breaking the seasons out into groups of three months. For instance, meteorological fall lasts precisely 91 days each year, going from September 1 through November 30.

Meteorological winter begins on December 1 and continues until the end of February, a date that varies depending on if it is a leap year. Meteorological spring starts March 1 and continues through May 31. Meteorological summer begins on June 1 and lasts through August 31.

Difference Between Fall and Autumn