Though there were few great cities on Earth where men could not see one of the silver ships glittering against the zenith, after a little while they were taken as much for granted as the sun, moon or clouds.
Up from the heart of the spreading moon-glow a tiny spark began to climb towards the zenith.
There are no more uses of "zenith" in the book.
Show samples from other sources
He met her when her career was at its zenith.
...and the sun passed the zenith and started down.