More head canon ideas....The moon has two sides, the light and dark side. For the light side to exist the sun must come first. Which is why Luna is the younger sister. Without the sun, the moon would be enshrouded in eternal darkness. Nightmare Moon is the manifestation of that dark side.Fausticorn: [link] Celestia: [link] Luna: [link] Twilight: [link] Chrysalis: [link] Cadance: [link]