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Iceland Mag


A rare double lunar rainbow seen by Stykkishólmur town in West Iceland

By Staff

  • A double moonbow Lunar rainbows are very rare due to the extremely specific conditions needed for their formation. The second rainbow was extremely faint, but can be discenred above the main rainbow. Photo/Víðir Björnsson.

A rare lunar rainbow, or moonbow was seen near the town of Stykkishólmur on the Snæfellsnes peninsula in West Iceland late last night. Photographer Víðir Björnsson caught the phenomena on film, and posted the photograph on Facebook. He added in comments that the moonbow was actually a double-rainbow, since a very faint second rainbow could be seen just above the main rainbow. The second moonbow can just barely be made out in the photograph, but Víðir says it was well visible at the time.

Lunar rainbows are formed in exactly the same way as regular rainbows, except they are formed by moonlight. The fact that moonlight is much fainter than sunlight, and that it is dark at night makes it very hard to see lunar rainbows. Their colours are also usually too faint to note, making them look white. Therefore lunar rainbows are sometimes also called white rainbows. However, the colours always appear in long exposure photographs.

Lunar rainbows are most likely to be seen at or near a full moon, when the brightness of the moonlight is greatest. For a moonbows to appear the moon must be low in the sky, and the sky very dark. This means a moonbow is best observed 2 to 3 hours before sunrise or 2 to 3 hours after sunset. Finally, for a moonbow to appear there needs to have rain or mist in the opposite direction in the sky from the moon.

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