The poem sketches a crowded beach in a few quick strokes. The bodies "at the sea" are sweaty, almost animal, and the chairs all tilt toward the sun, which the speaker calls "that dog." It's a funny, slightly irreverent image: the sun as a panting, attention-grabbing pet that everyone follows around.
Then the tone shifts. A ship, apparently seen from the shore, makes the speaker "understand many things," though the poem never says what. That gap feels deliberate. The insight is large but wordless, the kind of thing that arrives while you stare at the horizon. The last image, eyes "full of it all / like cheap moons," could suggest eyes round and glassy from taking in so much, though the "cheap" keeps things humble.
The title adds a twist: these sweaty humans are "celestial bodies" too. The mood is light, observant and a little dreamy, mixing mild mockery with quiet wonder.