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autumnal equinox

[ aw-tuhm-nl ee-kwuh-noks, ek-wuh-noks ]
/ ɔˈtʌm nl ˈi kwəˌnɒks, ˈɛk wəˌnɒks /
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noun

See under equinox (def. 1).
Also called au·tum·nal point . the position of the sun at the time of the autumnal equinox.

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Origin of autumnal equinox

First recorded in 1670–80

Words nearby autumnal equinox

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2021

VOCAB BUILDER

What is the autumnal equinox?

The autumnal equinox (also called the fall equinox) is one of the two equinoxes—the times of the year when the amount of daylight and nighttime hours are just about of equal length. The two equinoxes occur around March 20–21 and September 22–23.

The equinoxes occur on these days, but an equinox is not the whole day—it is the moment when the sun is directly above Earth’s equator. The term equinox can also refer to the position of the sun at this moment, and the term autumnal equinox can refer to the position of the sun at the moment considered the autumnal equinox. This can also be called the autumnal point.

The autumnal equinox is traditionally considered to mark the start of fall, while the vernal equinox is considered to mark the start of spring. In the Northern Hemisphere, the autumnal equinox occurs in September and the vernal equinox occurs in March. In the Southern Hemisphere, it’s the reverse.

In contrast, a solstice is one of the two times of the year when the positioning and tilt of Earth relative to the sun results in the most amount of daylight time or the least amount of daylight time in a single day.

There are two solstices during the year: one that occurs around June 20–22 (usually June 20 or 21) and one that occurs around December 20–23 (usually December 21 or 22). In the Northern Hemisphere, the summer solstice occurs in June and the winter solstice occurs in December. In the Southern Hemisphere, it’s the reverse.

Example: Some leaves start changing color around the time of the autumnal equinox, but some stay green for much longer.

Where does autumnal equinox come from?

The first records of the term autumnal equinox come from around 1530. The word autumnal means “of or relating to autumn (fall).” The word equinox comes from the Latin aequinoctium, meaning “the time of equal days and nights,” from equi-, meaning “equal,” and nocti-, meaning “night.”

An equinox is a moment, not an entire day. Since Earth is in motion, the exact positioning considered an equinox only happens for a moment. However, the word is most commonly used to refer to the day on which this happens. On most calendars, these days are used to mark the beginning of spring and fall similar to how the days of the two solstices are used to mark the beginning of summer and winter.

While the day of an equinox has equal amounts of daylight and darkness, the days on which the solstices occur are known for being the longest and shortest days of the year in terms of daylight. During the summer solstice, Earth is tilted toward the sun and receives sunlight for the longest time, resulting in the longest day of the year. During the winter solstice, Earth is tilted away from the sun and receives sunlight for the shortest time, resulting in the shortest day of the year. After the winter solstice, the days start getting longer (receiving more daylight time), reaching an equal amount on the day of the vernal equinox. After the summer solstice, the days start getting shorter (receiving less daylight time), reaching an equal amount again on the autumnal equinox.

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What are some synonyms for autumnal equinox?

  • fall equinox

What are some words that share a root or word element with autumnal equinox

What are some words that often get used in discussing autumnal equinox?

How is autumnal equinox used in real life?

The autumnal equinox is popularly associated with the first day of fall.

 

 

Try using autumnal equinox!

True or False?

The autumnal equinox occurs on the shortest day of the year.

Example sentences from the Web for autumnal equinox

British Dictionary definitions for autumnal equinox

autumnal equinox

noun

the time at which the sun crosses the plane of the equator away from the relevant hemisphere, making day and night of equal length. It occurs about Sept 23 in the N hemisphere (March 21 in the S hemisphere)
astronomy
  1. the point, lying in the constellation Virgo, at which the sun's ecliptic intersects the celestial equator
  2. the time at which this occurs as the sun travels north to south (23 September)
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for autumnal equinox

autumnal equinox
[ ô-tŭmnəl ]

See under equinox.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
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