Rainbows Only Appear During the Day
We've been talking about how water and sunlight are the ingredients for a rainbow. If this is the case, then it should follow that rainbows can only pop out during the day. But they can actually occur at night, too. An evening rainbow is called a moonbow, or lunar rainbow. Moonbows are created when light reflected by the moon hits water droplets in the air. Before you think a moonbow can't be a rainbow if it's made from water and moonlight (not sunlight), remember that moonlight is actually reflected sunlight; the moon doesn't give off any light [source: National Geographic].
For a moonbow to form there needs to be a full or nearly full moon. And, as we said earlier, some water in the air. Because tropical areas such as the Caribbean and Hawaii tend to have showers lasting well into the evening, moonbows most frequently appear in these locales. All of the same colors in a rainbow are present in a moonbow. But moonbows are pretty faint, since moonlight is so much dimmer than sunshine. Since our eyes can't perceive colors when the lighting is dim, we see moonbows as white. Interestingly, though, photos of moonbows do show their colors [sources: Live Science, National Geographic, Science Kids].