The Autumn Equinox Means Fall Has Officially Arrived


The Autumn Equinox Means Fall Has Officially Arrived

September 22, 2017

Hang up your swimsuit and get ready to wrap a scarf around your neck because cooler weather is coming. Today, Sept. 22, is the Autumn Equinox. Astronomically, it marks the official end of summer and the beginning of fall. So although it may still feel like summer in Houston for another month or so, we will officially cross over to a new season today.

Equinoxes are not a full-day event. Instead, the equinox occurs at the exact moment the sun crosses directly over the Earth’s equator. In Houston, the equinox will take place at 3:01 p.m. local time, and the crossover for the fall seasons happens at the same moment all around the globe.

Is the fall equinox always on Sept. 22?

The fall equinox usually occurs on Sept. 22 or 23, but very rarely, it can fall on Sept. 21 or Sept. 24. Fun fact: A Sept. 21 equinox has not happened since the year 1000, but it will happen twice this century in 2092 and 2096. A Sept. 24 equinox occurred in 1931, and the next one won’t take place until 2303.

These dates vary because of our calendar and the fact that it takes for Earth about 365 and 1/4 days to complete its orbit around the Sun. Each September equinox occurs about 6 hours later than the previous year’s, so eventually, the date moves by a day.


Are the days and nights now equal in length?

The word equinox originates from the Latin words aequus, which means equal, and nox, which means night. It has become a common misconception that everyone on Earth will experience 12 hours of daylight and 12 hours of night on the equinox. But contrary to popular belief, night and day are not equal yet; the day is still a few minutes longer, and they won’t be equal in Houston until Sept. 25.

Most places on Earth will enjoy more than 12 hours of daylight today because of two reasons: the way sunrise and sunset are defined, and atmospheric refraction of sunlight. It’s a bit of an optical illusion because the Earth’s atmosphere bends the sunlight, making the sun look like it’s above the horizon when it’s actually below the horizon line. You can witness a similar phenomenon by putting a pencil in a glass of water; the pencil will look like it’s split in two at the water line.


What is a Harvest Moon?

The full Moon closest to the Autumn Equinox is called the Harvest Moon, and it’s astronomically special because the length of time between moonrises becomes shorter. This year’s Harvest Moon will occur on Oct. 5.

Our Moon’s cycle lasts 29.53 days, and the Moon rises about 50 minutes later each day. But with the Harvest Moon, the difference is only 30 minutes. In earlier times, the early moonrise meant farmers could work outside and harvest crops for a longer time. At Sipipa, we think it means you have a good excuse to enjoy dinner out with your family!