equinoctial

/ˌikwəˈnɒkʃəl/

Other forms: equinoctials

If something happens right around the time of an equinox — the two days each year when day and night are of equal length — you can describe it as equinoctial.

If your birthday falls on the spring equinox, you can call it equinoctial, and you could also call the fall hurricanes in your coastal town equinoctial storms. In either case, the thing that makes something equinoctial is its proximity to the dates in the spring and fall when the Earth isn't tipped toward or away from the sun but is positioned so the equator lines up with it. The Latin roots are aequus, "equal," and nox, "night."

Definitions of equinoctial

1. adjective

   relating to an equinox (when the lengths of night and day are equal)
2. noun

   the great circle on the celestial sphere midway between the celestial poles
   synonyms: celestial equator, equinoctial circle, equinoctial line

   type of:

   great circle

   a circular line on the surface of a sphere formed by intersecting it with a plane passing through the center
3. adjective

   relating to the vicinity of the equator