月虹

1. Origins, structure, and basic meaning

• Structure: The spelling is 月虹, read げっこう, and it combines 月, meaning moon, with 虹, meaning rainbow.
• Basic usage: 月虹 is a moonbow, a faint nighttime rainbow formed when moonlight is refracted and reflected by water droplets.

2. Common pitfalls and similar expressions

• A lunar phenomenon distinct from a sunlight rainbow
  • Both examples use the form 月虹. It is formed by moonlight rather than daylight, with conditions such as waterfall spray or a bright full-moon night supplied by context.
• A report from near a waterfall and a full-moon photograph
  • 滝の近くで淡い月虹を見たという物語を聞いた。 — I heard a story about someone seeing a pale moonbow near the waterfall.
  • 写真家は満月の夜に現れた月虹を静かに撮影した。 — The photographer quietly captured a moonbow that appeared on the night of the full moon.