By Jonny Lupsha, Wondrium Staff Writer
Today marks the autumnal equinox for 2020, or the first day of fall, The Old Farmer’s Almanac reported. On this day, the Sun crosses the “celestial equator,” which is an extension of the Earth’s equator into space. In places north of the equator, cold fronts usually follow.
According to The Old Farmer’s Almanac, September 22 marks the autumnal equinox—also called the September equinox or the fall equinox—in the Northern Hemisphere. “The autumnal equinox is the astronomical start of the fall season in the Northern Hemisphere and of the spring season in the Southern Hemisphere,” the article said. “After the autumnal equinox, the Sun begins to rise later and nightfall comes sooner. This ends with the December Solstice, when days start to grow longer and nights shorter.”
Each of the four seasons on Earth brings a new equinox, affecting the length of time that the Sun shines, often coinciding with noticeable temperature shifts. As fall approaches, colder weather usually begins to set in—but what about the other seasons?
From March to September
The seasons of the Earth occur because of the planet’s tilt as it rotates on its axis. Each season causes an equinox.
“Equinox literally means ‘equal night,’ which is to say that every location on Earth except the North and South Poles experiences 12 hours of darkness and 12 hours of daylight,” said Professor Eric R. Snodgrass, Director of Undergraduate Studies for the Department of Atmospheric Sciences at the University of Illinois at Urbana–Champaign. “Starting on March 21, the vernal or spring equinox, the Sun’s rays shine directly on the equator. On that day at noon, if you were standing on the equator, you would be shadowless.”
Interestingly enough, the Sun also rises on the North Pole on March 21 and doesn’t set for six months. Additionally, it’s one of the record-holding days for car accidents. This is because the Sun sets exactly in the west after rising directly from the east, obscuring the vision of drivers commuting on east-west roads.
“By June 21, the Sun’s rays reach their northernmost latitude and strike directly in the Tropic of Cancer, and summer begins in the Northern Hemisphere,” Professor Snodgrass said. “This day is called the summer solstice—solstice means ‘Sun stop.’ This is the farthest north the direct rays of the Sun will ever reach.”
If you live in the north Arctic Circle, the Sun doesn’t set at all on June 21, he said.
Cooling Off in the Fall and Winter
“As the autumnal, or fall equinox, arrives, the Sun, which has been out on the North Pole for six months, finally sets,” Professor Snodgrass said. “Six months of darkness arrives. The Southern Hemisphere starts spring, and the Sun rises on the South Pole to begin six straight months of sunshine there.”
Winter arrives at the winter solstice on December 21. Professor Snodgrass said that it’s the shortest day of the year in the Northern Hemisphere in terms of daylight hours.
“On this day, the Sun’s rays are direct on the Tropic of Capricorn, which is located at 23-1/2 degrees south,” he said. “Where I live in Champaign, Illinois, the Sun at noon on this day is roughly 30 degrees above the horizon.”
The 2020 year may have seemed like a long year to a lot of people, but with the onset of the autumnal equinox, it’s finally in the home stretch before the next calendar year begins.
Professor Eric R. Snodgrass contributed to this article. Professor Snodgrass is the Director of Undergraduate Studies for the Department of Atmospheric Sciences at the University of Illinois at Urbana–Champaign, where he also received his master’s degree. Previously, he earned his bachelor’s degree in Geography from Western Illinois University.