Finding and Photographing Rainbows

Part 6. Rainbow Planner

Season

Now we know that rainbows form when sufficiently large droplets of water are in the air, and direct sunlight hits them. That means you're unlikely to observe rainbows in cold climates, because atmospheric moisture is likely to be frozen. Bright sunlight is a must for bright rainbows, so anticipate more rainbows in spring and summer than in fall and winter.

Storms

Receding rain storms tend to have falling rain in their trailing edge, where it can be exposed to newly-revealed sunlight and form rainbows. Approaching storm clouds, on the other hand, tend to overshadow the advancing wall of rain, so no sunlight hits the droplets and rainbows are less likely to form.

Terrain

Some locales experience very predictable afternoon storms marching away from direction of the sun, followed by clearing, sunshine, and rainbows. These are ideal locations for photographing rainbows, assuming there are subjects of interest for composing images. Less than ideal are locales where the afternoon storms move toward the sun, or where the storms are not regular or predictable. Good terrain for rainbows allows you to see clearly toward the horizon opposite the sun, so you have a chance of photographing the end of the rainbow. Finally, good rainbow terrain allows you to move freely to a location where the rainbow is in a desired position for your composition. Ideally, you can scout good locations and subjects on days without storms, then return with full knowledge of your objective.

Angle of Sun

If the sun is directly overhead, our 42-degree paper cone will point straight into the ground, so no rainbow will be visible (unless we're off the ground looking down at spray). The sun must be at 42 degrees above the horizon or lower before the rainbow arc starts to rise above the opposite horizon. Therefore, look for rainbows in the morning or afternoon, depending on the season and your location.

Those equipped with portable GPS units may already have a solar position calculator in hand, telling exactly what elevation and azimuth (direction) the sun will be at a given time. These use standard astronomical data which is also available on the web from numerous sources, including the U.S. Naval Observatory (http://aa.usno.navy.mil/data/). Then you need a compass to find the direction, estimate the angles. wait, that's too hard.

Pinpointing your Rainbow


Locating a Rainbow (click to enlarge)
As the storm passes, wait until you can see your shadow, however faintly. The good news is that a receding storm (good candidate for rainbows) will usually expose you to sunlight before the rainbow will appear. Once you can see your shadow:
  1. Hold your thumb at a 42 degree angle from your index finger. Well, don't measure the angle, just estimate half a right angle (L-shape). This will be 45 degrees, which is close enough.
  2. Now point your index finger at the shadow of your head, while sighting down the finger like a pistol. It's best to hold your arm fully extended to make step #3 easier.
  3. Pivot your wrist while keeping the index finger aimed.
  4. Your thumb will now trace the direction of the rainbow's arc.

While this method may seem imprecise, it can indicate with surprising accuracy the location of the potential rainbow. Normally, you'll be most interested in the location where the rainbow intersects the ground. If there isn't a good subject there, consider moving to a new spot so that the rainbow's end falls directly on, or near, an interesting subject.

The last step in the process is to hope that conditions lead to the formation of a strong rainbow! Send and let us know if you have any good tips for finding and photographing rainbows. Happy hunting!

To return to the beginning of this article, see Part 1. Finding Rainbows.


Updated 20-aug-11   Contents copyright © 2001 - 2011 PhotoCentric.Net, All Rights Reserved