Tiffany knew it was gibbous because she’d read in the Almanack that gibbous meant what the moon looked like when it was just a bit fatter than half full, and so

Tiffany knew it was gibbous because she’d read in the Almanack that gibbous meant what the moon looked like when it was just a bit fatter than half full, and so she made a point of paying attention to it around those times just so that she could say to herself: “Ah, I see the moon’s very gibbous tonight . . .” It’s possible that this tells you more about Tiffany than she would want you to know.