Here are 5 things to know about the autumnal equinox 2022, the debut of astronomical fall

Roberto Villalpando, Austin American-Statesman
·3 min read
Our home planet, Earth, as seen at 6:30 a.m. Tuesday, the day before the fall equinox. During the autumnal equinox, the sun shines directly on the equator, and the northern and southern hemispheres get the same amount of rays.

For traditionalists who still use the sun to tell time, fall finally arrives Thursday with the autumnal equinox. Before we break out the pumpkin carving tools or go thrift shopping for Halloween costumes, here are five things to know about this annual astronomical event:

1. What is the autumnal equinox?

During the autumnal equinox, the sun shines directly on the equator, and the northern and southern hemispheres get the same amount of rays. The alignment officially occurs this year at 8:03 p.m. Thursday for those living in the Central time zone. Clouds notwithstanding, Austin will get about 12 hours and 8 minutes of daylight.

2. What does equinox mean?

The Earth spins on a tilted axis, which means that as the planet orbits the sun, it is leaning toward or away from the sun — thus, giving us seasons. But twice in the course of that yearlong trip around the sun, the Earth is not inclined toward or away from the sun. Each of those instances is an equinox, which is derived from the Latin words for equal (aequus) and night (nox).

But after the autumnal equinox, the northern hemisphere of the Earth begins to tilt away from the sun, so nights will get longer and days will grow shorter until the winter solstice, which will be on Dec. 21 at 3:48 p.m. in Austin.

More: Farewell flip-flops, hello pumpkin spice: The autumnal equinox is Wednesday

3. Why is it important?

For ancient societies, the autumnal equinox marked the end of summer and the vernal (or spring) equinox marked the end of winter, which helped people track time-sensitive activity, such as when to plant crops. According to the Farmers’ Almanac, the changing colors of the leaves on deciduous trees is actually triggered by the shorter days with reduced amounts of daylight.

4. Didn’t autumn start already?

Yes, but it might not feel like it has — Austin has had an unusually hot and dry start to fall. Meteorologically speaking, fall is the months of September, October and November, yet September in Austin this year already has an average temperature of 83.5 degrees, which is about 1.5 degrees warmer than normal.

The city has already recorded 68 days of 100-degree weather, but temperatures in Austin are expected to return to triple digits. The National Weather Service forecast for Austin calls for sunny skies on Thursday with a high of 102 and a high of 101 degrees on Friday.

Looking at more than 120 years of data, Austin historically averages about 15 days of triple-digit temperatures each year with only one in September. But if you look at just the data since 2000, as the effects of climate change have become more apparent, that annual average jumps to 35 with three of them in September. Last year, Austin had seven days with triple-digit temperatures.

5. Forecasters’ fall started Sept. 1.

Meteorologists prefer a calendar in which the seasons start on the same days every year primarily because it can provide consistency in record-keeping. But the Earth's elliptical orbit around the sun makes it hard for the planet's position to conform to a fixed calendar — consequently, the autumnal and vernal equinoxes, as well as the winter and summer solstices don’t fall on the same day every year. The autumnal equinox falls on Sept. 23 next year, but then it goes back to Sept. 22 in 2024.

This article originally appeared on Austin American-Statesman: What is an equinox? Five things to know about the start of autumn