Rainbows are beautiful things to behold and are generally quite rare. But there is a rainbow so elusive that many do not know it exists and most have never actually seen one. This rainbow can only be captured by the light of the moon… it’s a moonbow or lunar rainbow. This particular rainbow is a perfect subject for photography. It is visible to the naked eye but can be truly captured on a film or digital camera set to a longer exposure. This is one of those rare instances that the camera can out-perform the human eye. On a really bright night, your eyes see a silver band with maybe the faintest color. Depending on how bright the night is, the camera can capture almost all the rainbow’s colors.
First, how do you even find a lunar rainbow? Think of how many rainbows you see in the course of a 30-day month. Now consider that you only have roughly 8 to 10 days to see a lunar rainbow in that same period of time. This is a very short window. Also, just like with daytime rainbows, lunar rainbows require certain conditions. The sun or moon must be bright and unobstructed and at a 45-degree angle to moisture in the sky for a rainbow to appear. The moon is only bright enough to produce a good rainbow 8 to 10 days a month. Rainbows are hard enough to find in the daytime but at night, it’s even more difficult.
When selecting on a location, first determine at what time the moon rises or sets. Second, determine the direction that it rises or sets in order to set your composition accurately. Finally, considering that you’ll be shooting close to a full moon, determine at what time the sun rises or sets. It’s simple to gain this information using apps, our phones, or websites. When shooting a lunar rainbow, the moon will be behind you and the sun will be preparing to rise in front of you. Obviously if the light coming over the horizon from the sun gets too bright, you’ll lose your moonbow.
A more difficult way to find a moonbow that can produce some amazing results is to search for one at the edge of a rainstorm. If you’re shooting after the sun sets and the moon rises, you’ll be looking for compositions where the rain is in the west and it’s clear in the east. As it gets darker, it’s harder to tell where there is clear weather but look for stars or, when the moon comes up, its light can also help. If you are shooting at moonset, this is reversed. You are looking for clear skies in the west with moisture in the east. This procedure is difficult because it requires moving and composing on the fly in whichever location you encounter a rainbow.
I suggest scouting during the days for possible locations along a road you may be traveling and then do some nighttime scouting to determine whether or not there’s too much light pollution. City lights that are too bright will blow out your sky before you can expose for the moonbow. A good way to test for light pollution is to go out on a moonlit night and expose for the landscape by moonlight. If the landscape can be captured brightly and you don’t notice major light pollution, the location should be okay.
We’ve probably all heard the phrase “No rain, no rainbows”. Without trying to be a “negative Nancy” on such a positive outlook on life, let me say that phrase is a lie. Living in Hawaii (the land of rainbows), I can tell you that rainbows do occur without rain. You just need to find a waterfall. This makes hunting for moonbows quite easy. Find a waterfall that creates enough mist that is orientated in the right direction, show up at the right time on a clear night, and you’ve got your moonbow. There are many famous waterfalls around the world that have already been found to have moonbows… such as the majestic Yosemite falls in spring under the full moon.
To be continued How to Photograph a Moonbow – Part 2