Cryptic crossword No 3,429

Thanks Kempley for a lovely tribute to a wonderful cosmic event! Finding the answer wasn’t always straightforward but the key was plain to see (eventually.) Lots of fun along the way with some sparkling individual clues, my faves being 9a, 12a, 21a, 2d, 8d, 15d, & 19d. Oh and 24d, once I got the synonym. Small q below…