Yes, ZENITHS is a Scrabble word!

Letter values in Scrabble US: Z 10, E 1, N 1, I 1, T 1, H 4, S 1.

Is it a valid word?

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

the point above the observer that is directly opposite the nadir on the imaginary sphere against which celestial bodies appear to be projected