Autumn Equinox 2022: Autumn is characterized by falling leaves and cooler temperatures. The autumnal equinox, also known as the September equinox, marks the beginning of the astronomical fall season in the Northern Hemisphere. The autumnal equinox can occur anytime between September 21st and September 24th. This year, the autumnal equinox falls on September 22 at 8:04 pm CDT (September 23 at 6:34 am in India).
Earth has two types of seasons, meteorological and astronomical. The tilt of the Earth’s axis with respect to the Sun-Earth plane and the position of the planet around the Sun cause the “astronomical” seasons.
“Meteorological seasons” are based on seasonal temperature variations modulated by fluctuations in the amount of solar radiation received at the Earth’s surface over the course of a year. Every year, the spring weather season begins on March 1 and ends on May 31.
The Earth’s tilt on its axis and the planet’s constant motion as it orbits the Sun result in the equinoxes and solstices. September to November is considered autumn.
What is Equinox?
An equinox is an astronomical event in which the Sun shines directly on the equator, resulting in nearly equal amounts of day and night all over the world except at the North and South Poles. At the poles, the sun orbits the horizon roughly throughout the day, says Alphonse Sterling, an astrophysicist at NASA’s Marshall Space Flight Center in Huntsville, Alabama, the space agency says on its website.
An equinox is an event in which the Earth’s subsolar point passes through its equator. The subsolar point on a planet is the point where the Sun is perceived to be directly overhead, and where the Sun’s rays strike the planet exactly perpendicular to the surface.
The Earth’s journey around the Sun drives the astronomical seasons, while annual temperature cycles guide the meteorological seasons.
Equinox occurs as the Earth tilts on its axis as it revolves around the Sun. On the equinox, Earth’s axis is tilted 23.5 degrees from the plane of its orbit.
The Science Behind the Autumnal Equinox
The autumnal equinox marks the first day of fall or autumn in the Northern Hemisphere. Meanwhile, in the Southern Hemisphere, fall begins in March. The September equinox is called the spring equinox in the Southern Hemisphere.
Similarly, the March equinox is called the spring equinox in the Northern Hemisphere.
Equinoxes happen only twice a year. Because the Earth’s axis is tilted with respect to the Sun-Earth plane, the Sun shines equally on the Northern and Southern Hemispheres, and this tilt results in the seasons. However, at the spring and autumn equinoxes, the sun shines almost equally in the northern and southern hemispheres.
On the first day of solstice in the Northern Hemisphere, the Earth is perfectly aligned sideways to the Sun. In other words, the Sun is above the Earth’s equator, moving from north to south. As a result, on an equinox, the length of day and night are almost equal all over the world.
After the autumnal equinox, the sun gradually rises later and sets earlier in the Northern Hemisphere. It shortens the days and lengthens the nights. Meanwhile, in the Southern Hemisphere, the sun begins to rise earlier and set later, after the September equinox, which marks the first day of spring for anyone living south of the equator.
In the Northern Hemisphere the spring or vernal equinox occurs on March 20 or 21. This year, the March equinox, or the astronomical start of spring in the Northern Hemisphere, occurred on March 20.
According to NASA solar scientist Mitzi Adams, a kind of twilight will prevail over the North Pole from the autumnal equinox through October, NASA said on its website. This is because in the next few days after the autumnal equinox, the sun will go below the horizon.
The full moon in September is called the harvest moon because it is the closest full moon to the fall equinox, also known as the fall equinox.
An equinox is a moment in time
Equinoxes are generally considered to be a one-day event. However, when the Sun crosses the celestial equator, which is an imaginary line in the sky above the Earth’s equator, it is an instantaneous event that occurs in an instant.
An equinox is when the Earth’s axis does not tilt or tilt toward the Sun. After the autumnal equinox, the Northern Hemisphere has an earlier sunset and later sunrise.
Are the days and nights exactly equal at the equinoxes?
The term equinox comes from the Latin words “aequus”, meaning “equal”, and “nox”, meaning “night”. However, it is a common misconception that night and day are completely equal at the equinox.
Day and night are not exactly 12 hours each at the autumn or spring equinox. According to the National Weather Service, in some places in the Northern Hemisphere, due to refraction of sunlight, the sun appears to be above the horizon when it is actually below it.
People living farther from the equator experience longer days.
Although the Sun’s center disappears 12 hours after sunrise, the day begins just before the Sun’s center rises because the Sun’s upper edge rises above the horizon before the center. The same is true of sunset, because it does not occur until the entire sun has completely sunk below the horizon. As the upper edge of the Sun sets below the horizon after the center, night begins shortly after sunset.
This is why the days are a little longer when the autumnal equinox begins, and after a few days, equal days and nights begin to occur.
In most parts of the world, the equinox day is slightly longer than 12 hours.
What is Equilix?
The equinox is the date when day and night are actually equal, and falls a few days before the vernal equinox and a few days after the autumnal equinox in both hemispheres. That is, Equilix falls a few days after September 22-23 in the Northern Hemisphere.
Equinoxes do not occur on a fixed day
The autumnal equinox usually occurs on September 22 or 23. But, sometimes it can happen on 21st or even 24th September. It takes 365.25 days or 365 days and 6 hours for the Earth to revolve around the Sun, meaning 6 equinoxes occur. hours later than the previous year. The Gregorian calendar does not consider those six hours. Instead, these six hours count as an extra day in a leap year. Due to leap years, the day of the equinox was reset to September 22 or 23. The last autumnal equinox occurred on September 24, 1931, and the next time it will occur is in 2303.
The fall equinox is prime time to see the Northern Lights
Aurora Borealis refers to a spectacular display of colorful lights in the night sky. The autumnal equinox in the Northern Hemisphere is prime time to see the aurora borealis, or northern lights. This is because at the equinox, the frequency of geomagnetic storms is twice the annual average.
At the equinoxes, particles of the solar wind or plasma can reach Earth’s atmosphere through our geomagnetic field due to Earth’s axial tilt, and this interaction results in strong geomagnetic storms.
Particles of plasma interact with atoms of oxygen, nitrogen and other elements in the atmosphere and emit photons of different wavelengths, resulting in the beautiful colors of the aurora.
Harvest Moon around the autumnal equinox
The first full moon that occurs in September is called the Harvest Moon. After the autumnal equinox, the moon rises early in the evening, and as a result farmers can work longer hours.
In Britain and in churches, the Harvest Festival is celebrated on the Sunday closest to the Harvest Moon.
Significance of autumnal equinox in ancient times
According to the French Republican calendar, the autumnal equinox marked the official start of each new year between 1793 and 1805. This is because the French monarchy was abolished on the day before the equinox in 1792. From 1793 to 1805, the year began when the autumnal equinox fell on the first day of each at the Paris Observatory.
The sun rises in the east and sets in the west at the equinox
At the autumn and spring equinoxes, the sun rises in the east and sets in the west, meaning that the cardinal compass point is 90 degrees or straight to the east and west, respectively.
The vibrant reds and yellows of autumn
Chemicals such as flavonoids, carotenoids, and anthocyanins become more prominent in leaves after the autumn equinox, while chlorophyll declines. It produces vibrant ambers, reds and yellows in autumn.
The word ‘autumn’ is of French origin
Autumn is derived from the French word ‘automne’. Also, fall, used to describe the autumn season, is an abbreviation of the phrase “falling of a leaf.”
Cold weather in the Northern Hemisphere after the autumnal equinox
After the autumnal equinox, temperatures cool in the Northern Hemisphere, resulting in a cooler climate.
Interesting traditions and festivals during the autumn equinox
The beginning of astronomical autumn in the Northern Hemisphere is celebrated with holidays, traditions, folklore and festivals.
In the United Kingdom, followers of Wicca gather at Stonehenge, the world’s most famous prehistoric monument, and at Castlerick, another megalithic stone circle near Keswick in Cumbria. They gather at these prehistoric sites to watch the sunrise on the equinox day.
Pagans with different religious beliefs from others around the world celebrate the autumn equinox with a harvest festival called Mabon, a time to practice apple magic. In apple magic, a person peels an apple, holds it in a long piece, and drops it on the ground when it comes out. The letter formed is the first initial of the name of the person’s real girlfriend. Pagans also associate apples with immortality.
In Japan, people celebrate Higan, a six-day Buddhist festival in both September and March. Higan means “other shore” and refers to the spirit of the dead reaching Nirvana, which the Japanese remember by visiting, cleaning and decorating their graves.
On the day of the autumnal equinox in the Northern Hemisphere, afternoon sunlight bathes the west side of the main staircase of the Mayan pyramid of El Castillo, Mexico. It creates a shadow that follows the body of a 120-foot-long rattlesnake, crawling down. The shadow is called ‘Snake of Sunlight’.