Autumn Equinox

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Autumn Equinox

Type of Holiday: Calendar/Seasonal
Date of Observation: September 22 or 23
Where Celebrated: All over the world
Symbols and Customs: Balance of Light and Dark, Full Moon, Harvest Feasts
Related Holidays: Harvest Home, Higan, Mabon, Michaelmas, Mid-Autumn Festival


The English word equinox comes from the Latin word equinoxium, meaning "time of equal days and nights." The word equinox refers to the two days of the year when night and day are equally long, the autumn equinox and the VERNAL EQUINOX . In the northern hemisphere, the autumn equinox occurs on September 22 or 23 and marks the beginning of the fall season. From this day forth the days will grow shorter and shorter until the time of WINTER SOLSTICE. After that time, the days will grow longer, but they will still be shorter than the nights until the arrival of the VERNAL EQUINOX on March 21 or March 22.

This BALANCE OF LIGHT AND DARK occurs only on the equinoxes. The equinoxes are also marked by other interesting celestial occurrences. Since ancient times, people who watched the sky have noticed that the sun's daily path across it varies throughout the year. The sun traces an arc that falls lower in the sky, or further south, in the fall and winter, and higher in the sky, or further north, in the spring and summer. Although the sun always rises in an easterly direction, and sets in a westerly direction, the equinoxes are the only days on which the sun rises due east and sets due west. Moreover, on the equinoxes, the sun passes directly overhead in the equatorial zones. In astronomical terms, this happens because the ecliptic intersects the celestial equator, an imaginary line in the heavens that represents a projection of the earth's equator onto the dome of the sky. The ecliptic is the name scientists have given to the plane in which the earth and the other planets of our solar system orbit the sun. When the ecliptic and the celestial equator meet, the sun crosses directly overhead in the equatorial zones.

In the northern hemisphere the autumn equinox marks the beginning of fall and the vernal equinox marks the beginning of spring. In the southern hemisphere, the September equinox kicks off the beginning of spring, and the March equinox the beginning of autumn. This difference in the seasons between the two hemispheres is caused by the fact that the earth does not rotate on an axis that runs perpendicular to the line joining the earth and sun. Instead, the earth's axis is tilted twentythree degrees in one direction. As the earth moves through its yearly rotation around the sun, this tilt points the northern hemisphere towards the sun during one half of the year and the southern hemisphere towards the sun during the other half. The resulting difference in the exposure to the sun's light causes the differences in the length of days and nights. The equinoxes mark the two days of the year on which the earth's tilt results in equal exposure to sunlight and darkness all around the globe. As the earth moves past the September equinox, the northern hemisphere enters that half of the year when the earth's tilt points it away from the sun. Hence the days will be shorter than the nights.

The Autumn Equinox marks the changing of the seasons, which people in all parts of the world have honored since ancient times. Many cultures divided the year into two seasons, summer and winter, and marked these points of the year at or near the summer and winter solstices, during which light and warmth began to increase and decrease, respectively. In pre-industrial times, humans survived through hunting, gathering, and agricultural practices, which depend on the natural cycle of seasons, according to the climate in the region of the world in which they lived. Thus, they created rituals to help ensure enough rain and sun in the spring and summer so crops would grow to fruition at harvest time, which was, in turn, duly celebrated. Vestiges of many of these ancient practices are thought to have survived in festivals still celebrated around seasonal themes.

The earliest observation of the equinoxes can be traced back to ancient times. Archeologists have discovered that some of Great Britain and Ireland's prehistoric stone monuments are aligned in special ways with the equinoxes and solstices. These structures were built several thousand years before the time of Christ (between 4000 and 1500 B . C . E .). Halfway around the world in South America, the ancient Mayan peoples also built great rock structures aligned to the movements of the sun. The great pyramid of Chichen Itza, for example, located in Mexico, casts a striking serpent-shaped shadow on the day of the spring equinox. Other Mayan structures line up perfectly with the autumn equinox. Archeologists speculate about the importance of these dates to ancient astronomers and priests, but no one knows how they were observed or celebrated by ordinary people.


Balance of Light and Dark

The balance of light and dark that occurs on the autumn equinox is a prominent feature of many celebrations. For example, the celebration of MABON calls attention to natural phenomena that characterize the fall, such as the growing darkness, cooler weather, and decline in nature's fertility.

The Christian observance of MICHAELMAS contains similar themes. This feast honors the archangel Michael, who strengthens the weak and protects the fearful. Old traditions recommend calling on Michael for aid in battle and for the power to resist the devil. His feast day, September 29, comes just as the nights are becoming longer than the days. This is the perfect time to remember Michael, who fights against the forces of darkness, inspires strength, and confers courage.

In Japan, some people observe a Buddhist ceremony known as HIGAN at the time of the autumn and spring equinoxes. The balance of light and dark on these dates is thought to represent the balance between this world and the next. In the ceremonies performed for this holiday, the living pay respects to the dead and clean family graves.

Full Moon

People the world over have noticed that the full moon that occurs around this time of year appears to be larger and rounder than other full moons. This appearance has generated much folklore and myth. Scientists today, however, know that the moon's apparent change in size is an optical illusion.

In the U.S. the full moon closest to the autumn equinox is known as the Harvest Moon. In past times, when farmers did not have a lot of machinery to rely upon, they often had to work late in the month of September to finish the harvest. Nature aided them by providing them with a special kind of full moon at that time of year. First, the full moon closest to the autumn equinox generally rises just as the light of sun is fading, permitting farmers to continue their work into the early evening. In addition, near the time of the autumn equinox, the time between each day's moonrise shortens considerably. This means that during the two days that follow the full moon, moonrise would also occur fairly early in the evening. The full moon closest to the September equinox was so handy to farmers that they dubbed it the Harvest Moon.

In many Asian countries, people celebrate a holiday known as the MID-AUTUMN FESTIVAL near the time of the autumn equinox. This holiday revolves around the celebration of the full moon that occurs at this time of year. People make time to go outside and enjoy the beauty of the moon and give thanks for the fall harvest.

Harvest Feasts

In the British Isles, an old folk holiday called HARVEST HOME took place around the time of the September equinox. In times gone by, when people harvested wheat, corn, and other crops by hand, the harvest occupied just about everyone in the village. So, when the villagers finished the last of the grain harvest, they celebrated with a communal feast. This traditional celebration continues today, though modern farm machinery has advanced the date of the holiday into August. The HARVEST HOME celebration is thought to have inspired both the American THANKSGIVING holiday and the Canadian Harvest Festival.

In addition to the continuing celebration of HARVEST HOME, some groups of people interested in reconnecting with ancient religions have revived the celebration of the equinox itself. Neopagans and Wiccans, people who follow a natureoriented religion loosely linked to ancient pagan beliefs and inspired by old European folk practices, often celebrate the Autumn Equinox. Some of them call the holiday MABON, after an old Celtic legend that they associate with the day. Their celebrations often feature an autumn feast consisting of foods representing the late summer and early fall harvest.


Brennan, Martin. The Stones of Time: Calendars, Sundials and Stone Chambers of Ancient Ireland. Rochester, VT: Inner Traditions, 1994. Cabot, Laurie. Celebrate the Earth: A Year of Holidays in the Pagan Tradition. New York: Delta, 1994. Henderson, Helene, ed. Holidays, Festivals and Celebrations of the World Dictionary. 3rd ed. Detroit: Omnigraphics, 2005. Krupp, E.C., ed. In Search of Ancient Astronomies. New York: Doubleday, 1978. Urlin, Ethel. Festivals, Holy Days, and Saints' Days. 1915. Reprint. Detroit: Omnigraphics, 1990.


NASA Science News Department

University of California at Berkeley's Center for Science Education
Holiday Symbols and Customs, 4th ed. © Omnigraphics, Inc. 2009
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