equinox

[ ee-kwuh-noks, ek-wuh- ]

noun

1. the time when the sun crosses the plane of the earth's equator, making night and day of approximately equal length all over the earth and occurring about March 21 vernal equinox, or spring equinox and September 22 autumnal equinox.
2. either of the equinoctial points.

equinox

/ ˈɛkwɪˌnɒks; ˈiːkwɪˌnɒks /

noun

1. either of the two occasions, six months apart, when day and night are of equal length See vernal equinox autumnal equinox
2. another name for equinoctial point

equinox

/ ē′kwə-nŏks′ /

1. Either of the two points on the celestial sphere where the ecliptic (the apparent path of the Sun) crosses the celestial equator .
2. ◆ The point at which the Sun's path crosses the celestial equator moving from south to north is called the vernal equinox . The vernal equinox marks the zero point in both the equatorial and ecliptic coordinate systems; horizontal angular distances (right ascension in the equatorial system and celestial longitude in the ecliptic system) are measured eastward from this point. The vernal equinox is also known as the first point of Aries because when first devised some 2,000 years ago this point occurred at the beginning of Aries in the zodiac. Because of the westward precession of the equinoxes, the vernal equinox is now located at the beginning of Pisces.
3. ◆ The point at which the Sun's path crosses the celestial equator moving from north to south is called the autumnal equinox .
4. Either of the two corresponding moments of the year when the Sun is directly above the Earth's equator. The vernal equinox occurs on March 20 or 21 and the autumnal equinox on September 22 or 23, marking the beginning of spring and autumn, respectively, in the Northern Hemisphere (and the reverse in the Southern Hemisphere). The days on which an equinox falls have about equal periods of sunlight and darkness.
5. Compare solstice

equinox

1. The twice yearly times when the lengths of day and night are equal. At equinox, the sun is directly over the Earth 's equator . The vernal equinox occurs about March 22 and the autumnal equinox about September 21.

Word History and Origins

Origin of equinox¹

First recorded in 1350–1400; Middle English, from Medieval Latin equinoxium, for Latin aequinoctium “the time of equal days and nights” (equivalent to aequi- + noct- + -ium ); equi-, nocti-, -ium

Word History and Origins

Origin of equinox¹

C14: from Medieval Latin equinoxium, changed from Latin aequinoctium, from aequi- equi- + nox night

Example Sentences

Rain warnings were in place over the weekend as summer officially drew to a close following the autumn equinox on Sunday afternoon.

From BBC

Astronomical autumn begins on Sunday, with the equinox occuring around lunchtime and, right on cue, the weather will start feeling more autumnal in the week ahead.

From BBC

Further yellow weather warnings for rain have been issued by the Met Office for Sunday - the day of the autumn equinox marking the end of summer - and Monday.

From BBC

With the autumn equinox on Sunday - 22 September - it seems that Mother Nature has decided to end summer right on cue.

From BBC

But, on the day of an equinox, the tilt of Earth's axis is perpendicular to the Sun's rays, producing a nearly equal amount of day and night all over the world.

From BBC

More About Equinox

What is an equinox?

An equinox is one of the two 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 word equinox can also refer to the position of the sun at this moment. This can also be called the equinoctial point. 

The equinoxes are traditionally considered to mark the start of spring and fall. In the Northern Hemisphere, the vernal equinox (or spring equinox) occurs in March and the autumnal equinox occurs in September. 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: Many ancient cultures recognized and observed the equinoxes as times that marked the change of the seasons.

Where does equinox come from?

The first records of the word equinox come from the 1300s. It 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 spring equinox. After the summer solstice, the days start getting shorter (receiving less daylight time), reaching an equal amount again on the autumnal equinox.

Did you know ... ?

What are some other forms related to equinox?

• equinoctial (adjective)

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

• vernal equinox
• autumnal equinox
• equinoctial point

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

• vernal
• spring
• autumnal
• fall
• sun
• Earth
• equator
• season
• first
• day
• night

What are some words equinox may be commonly confused with?

• solstice

How is equinox used in real life?

Equinoxes are most commonly discussed and observed as times to mark the changing of winter to spring and summer to fall.

Have you ever thought about what equinoxes and solstices look like from space?

In 2010 and 2011, SEVIRI on Meteosat-9 captured these 4 views of how sunlight fell on the Earth during the winter solstice, spring equinox, summer solstice, and fall equinox. pic.twitter.com/CrXF7imYpF

— NASA History Office (@NASAhistory) December 21, 2020

Reminder today is the Autumnal equinox (for us southerners) and vernal equinox for those north of the wall.

Autumn/Spring starts today (by some definitions)

We reach the equinox at 2:49PM AEDT (Sydney time) this afternoon and then we head for winter solstice! https://t.co/w4UzVfhPHf

— Rami Mandow 🏳️‍🌈 (@CosmicRami) March 19, 2020

10yo: wait a minute
10yo: 6 weeks after Groundhog Day is … the spring equinox
10yo: that’s the official start of spring!
10yo: Groundhog Day is a scam!!

— Anne Thériault (@anne_theriault) February 16, 2021

 

 

Try using equinox!

True or False?

The equinoxes occur on the longest and shortest days of the year.