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Equinox

Autumn Equinox: What is it?

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Here in the Northern Hemisphere the autumn equinox is an astronomical event that usually falls on the 22nd or 23rd of September and marks the first day of fall. The next autumnal equinox will occur on Wednesday, September 22, 2021. What, however, will occur as the summer and fall seasons change hands?

What is an Equinox?

On our calendar the autumn equinox or “fall equinox” is represented by a single day, however it is actually an event that can be recorded down to the minute. At whatever point it occurs, the equinox is the moment the geometric center of the sun passes through the celestial equator, an imaginary extension of the earth’s own latitudinal center.

How Many Equinoxes Are There Each Year?

Each year there are two equinoxes on earth. The spring equinox, also known as the vernal equinox, happens each year around March 21st. As with the autumn version, and as its name suggests, the vernal equinox features a nearly equal day/night period and the sun is likewise viewed rising due east and setting due west from most latitudes on earth. The difference being during the vernal equinox the sun crosses the earth’s equator moving north whereas in the autumn equinox the sun crosses the equator moving south.

When the autumnal equinox occurs, the sun can be viewed rising due east and setting due west across most of the globe, and day and night are nearly equal length. In fact, the word equinox descends from the latin words “aequus”, meaning equal, and “nox”, meaning night. From this point on, the days get progressively shorter until the winter solstice when the path of the sun as viewed from the northern hemisphere is furthest south. This again, affects day length.

What Happens During Summer and Winter?

In between the spring and fall equinoxes, are the June and December solstices. Taking place on 21 or 22 of December, the winter, or hibernal solstice boasts the shortest day of the year / longest night of the year. However, from this point onward the days get gradually longer and continue to do so until the summer solstice in June, which conversely touts the longest day/shortest night on the calendar.

How Do Equinoxes and Solstices Affect the Seasons?

One would think it has to do with the earth’s orbit of the sun. However, the Northern Hemisphere in December is actually closer to the sun than it is in July. The answer actually lies in the earth’s own axis. It isn’t in a vertical alignment with the sun, rather the earth is tilted at an angle of 23 and a half degrees relative.

Though the earth may be closer to the sun in December, the Northern Hemisphere is tilted away from the sun at this point, causing shorter days and colder temperatures, while the Southern Hemisphere experiences summer. Only two days out of the year see both sides of the equator, north to south, pole to pole, equally aglow, and those are either equinox day.

The earth’s unique tilt at the time of the autumn equinox also makes possible the Harvest Moon. We have all heard the term, but what makes the Harvest Moon special? It actually has nothing to do with the appearance in size or color of the moon at this time, but with its rising and duration. The moon’s orbit of the earth is elliptical and around the time of the autumn equinox this orbit lines up nearly horizontally across earth’s horizon. The result is a moon that rises nearly at dusk and remains nearly until dawn across several days. The term Harvest Moon came about because this early rising, lingering moon would provide farmers with more light to get their harvests done before the first frosts arrived. Despite the possibility of multiple full or partial moons occurring around this time, only the full moon that occurs closest to the fall equinox is considered the actual Harvest Moon.

How is the Autumn Equinox Celebrated?

Many cultures and civilizations across history have celebrated the autumn equinox and harvest moons. While many lauded the astronomical event itself, others still recognized it as a time of transition, endings and beginnings. Centuries ago, during the Shang Dynasty of China, the people would make offerings to the moon and celebrate a successful harvest season.

Harvest Moon and Mid-Autumn festivals are still celebrated in China and Vietnam today. In Japan, some Buddhists celebrate a holiday called Higan, on both the autumn and spring equinoxes, where disciples travel to their places of origin to pay respects to ancestors. Higan at its meaning is symbolic of crossing into the afterlife. In the west, the people of Britain have long held festivals giving thanks at harvest time. To this day Druids gather on Primrose Hill in London to celebrate the autumn equinox. These practices were brought to North America with British settlers and are still in abundance nationwide.

Though the equinox occurs in September, American Thanksgiving was originally a celebration of thanks after a successful corn harvest and thus can be attributed to the equinox traditions of their ancestors.

Indeed, the autumn equinox has not only a profound effect on daylight and climate cycles, but also helped to shape various cultures and civilizations. It is a time of finality and transition, of death and sustenance. The harvest gives life with its life, and the cycle continues on, it seems, as long as the sun is alight and the earth rotating in its orbit.

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