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

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

Now the spring equinox has passed, we're seeing more than 12 hours of daylight in most of the Northern Hemisphere.

From BBC

We've seen a combination of high solar activity and an effect that happens around the equinox that can boost the energy needed for aurora.

From BBC

It comes on the spring equinox which marks the first day of astronomical spring - although weather forecasters prefer to refer to meteorological spring which began on 1 March.

From BBC

By Thursday - the spring equinox - the warmer air will have spread further north, with most places expected to have temperatures in the mid-to-high teens, and 20C possible in the London area.

From BBC

Thursday's warm weather will coincide with the spring equinox, which marks the start of astronomical spring.

From BBC

When To Use

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.