Definition

1. Noun:
   • An astronomical event: An equinox is one of the two moments in the year when the Sun is positioned directly above the Earth's equator. At this time, the plane of the Earth's equator passes through the center of the Sun, resulting in nearly equal lengths of day and night across the planet.
   • An astronomical point: An equinox is also one of the two points on the celestial sphere where the ecliptic (the Sun's apparent path) and the celestial equator intersect.

Examples of Usage

• Noun:
  • The equinox occurs twice a year, in March and September.
  • Many ancient cultures built monuments aligned with the sunrise on the spring equinox.
  • During the equinox, the Sun rises due east and sets due west for all observers on Earth.

Advanced Usage

• "Vernal equinox": The equinox that occurs in March, marking the beginning of spring in the Northern Hemisphere.
  • The vernal equinox is a time of renewal and celebration in many cultures.
• "Autumnal equinox": The equinox that occurs in September, marking the beginning of autumn in the Northern Hemisphere.
  • The autumnal equinox brings cooler temperatures and shorter days.

Variants and Related Words

• Equinoctial (adj): Pertaining to an equinox or the celestial equator.
  • Equinoctial storms are a common weather phenomenon.
• Equinoctial point (n): Another term for the astronomical point of an equinox.

Synonyms

• Solstice (Note: This is a related but distinct astronomical event marking the longest or shortest day of the year, not a synonym for equal day and night).

Noun

1. (astronomy) either of the two celestial points at which the celestial equator intersects the ecliptic
2. either of two times of the year when the sun crosses the plane of the earth's equator and day and night are of equal length