Rainbows do occur at night
To see a moon rainbow, many conditions must coincide:
1. there must be a full moon,
2. the moon must be either rising or setting,
3. and there must be mist in the air because a rainbow is made up of the rays of the sun that are reflected inside raindrops – or, in this case, the rays reflected by the moon.
Moon rainbows are a rarity; there have been only a few in the past 50 years.