Yes, EQUINOXES is a Scrabble word!

Letter values in Scrabble US: E 1, Q 10, U 1, I 1, N 1, O 1, X 8, E 1, S 1.

Is it a valid word?

EQUINOXES is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

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
(astronomy) either of the two celestial points at which the celestial equator intersects the ecliptic

Also: equinoctial point.