What is the fall equinox? Astronomical season begins Sept. 22 this year
Fall officially begins on Sept. 22 with the autumnal equinox, but if you ask a meteorologist, fall starts three weeks earlier. Here is the reason for the equinox, which means equal day and night.
What is an equinox? The science behind the astronomical seasons explained
The vernal equinox marks the beginning of astronomical spring and occurs in the Northern Hemisphere around March 20th, whereas the autumnal equinox falls around September 22nd.
Fall begins in the Northern Hemisphere on Monday, Sept. 22, when Earth experiences equal day and night, known as the autumnal equinox.
While fall officially begins with the autumnal equinox, if you ask a meteorologist, fall starts three weeks earlier on Sept. 1.
Meteorological fall is based on Earth's annual temperature cycles or seasons. The three months in the Northern Hemisphere between the coldest and the warmest months, summer and winter, are what define meteorological fall from Sept. 1 to Nov. 30.
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Astronomical seasons are labeled as such because of Earth’s tilt, either away or toward the Sun.
NOAA's GOES-16 satellite photo of Earth on the equinox.
(NASA/NOAA / NOAA)
Dr. Tyler Richey-Yowell, a postdoctoral fellow at Lowell Observatory in Arizona, helps break down why it’s called an equinox, demonstrating with a pencil through a tangerine.
"You have your Earth, and it rotates on an axis, which is this pencil here. But it's not straight up and down as it orbits the Sun. It's actually tilted by 23 and a half degrees," Richey-Yowell said. "During parts of the year, the Northern Hemisphere is pointed right towards the Sun, that's our summer, and our summer solstice, when we get the most sun. And the opposite is the winter solstice, where we get the least amount of sun."
Equinox comes from the Latin "equi," meaning equal, and "nox" or night.
This graphic shows the Earth and Sun during the autumnal equinox.
(FOX Weather)
"The equinox is just when neither the Northern nor the Southern Hemisphere is pointed towards the Sun," Richey-Yowell said. "And so you get equal day and night during that time."
According to NASA, this year the autumnal equinox happens on Sept. 22 at 2:19 p.m. ET or 11:19 a.m. PT, marking the moment when the center of the Sun crosses the plane of our equator.