A Game of Syzygy and a Really Long Word

My father and I were playing a spirited game of Syzygy, a fast-paced crossword-building battle game, when I realized I had sufficient letters to build one of the longest words in the English language.  You can always look up the definition of that word if you're curious.

See those tiles with pictures of the sun, the moon, and the Earth?  Those are "wild" tiles and can be counted as any letter.  See if you can guess which letters fit the wild tiles.