If I had to guess, I'd say that he did it in a single exposure by taking a long exposure then covered the lens with a black card/lens cap, waited a few minutes, uncovered it a few seconds for the single exposure of the heavenly bodies, and closed his shutter.
At least, that's what I would do if I were trying to recreate this effect.
At least, that's what I would do if I were trying to recreate this effect.