I get a real kick out of hunting down crossword-clue explanations, and 'celestial body' is one of those deceptively simple clues that sends you down a few rabbit holes.
If you want the straightforward route, start with online clue databases like OneLook, Wordplays, or Crossword Nexus — plug in the clue or the pattern (e.g., ? ? ? ? for a four-letter fill) and you’ll see common solutions like STAR, MOON, SUN, PLANET, ORB, or COMET listed with usage examples. For deeper history and editorial notes, cruciverb.com keeps solver notes and index entries (some sections need subscription), and the New York Times' Wordplay column often explains tricky usages in themed puzzles. For print, I still flip through 'Chambers Dictionary' or 'The Crossword Solver’s Dictionary' to see archaic senses and variant spellings.
If the clue was cryptic, remember the definition usually sits at one end, and the rest is wordplay — so look for anagrams, hidden words, or charades. Forums like r/crossword and Stack Exchange’s Puzzling section are great for crowd-sourced breakdowns; I love seeing how one neat parsing can make the whole clue click.