Rainbows at Night? The Phenomenon Known as Moonbows

Chances are, you’ve likely seen many rainbows in your life, whether it’s the classic bow shape of colors painted across the sky or just a quick glimpse of rainbow colors peaking through the spray of a sprinkler on a hot summer day. When white light from the sun hits a water droplet, some of the light is reflected while some of it is refracted, or bent, out of the droplet.  The dispersion of the refracted light at varying angles can cause the appearance of the rainbow. While rainbows are something that we see during the day, a similar phenomenon occurs at night.

Moonbows, also known as lunar rainbows, are formed in a similar manner to your typical rainbows, but with a different light source.  When light that is reflected off of the moon’s surface hits moisture in the air, the white light can be refracted into the spectrum of colors that we typically see in a rainbow.  However, since the light reflected from the moon is much dimmer than the light from the sun, moonbows will appear much fainter than their daytime counterparts.  If you happen upon a moonbow, you may not be able to see the full spectrum of colors and instead may just see a faint white light.  This is because the dim light is usually not enough to excite the cone color receptors in our eyes.  However, long-exposure photography can allow you to see the rainbow colors of a moonbow more clearly.

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