Whenever you see one rainbow, look for another, because rainbows always come in pairs. Consider this example, photographed by Kamila Mazurkiewicz Osiak of Trzcianki, Poland, on April 13th:

©Kamila Mazurkiewicz Osiak 

"This huge double rainbow appeared after an intense rainstorm passed through our area," says Osiak. "It was raining so hard, it looked like the clouds were walking on the ground."

The bright inner rainbow is the primary bow, caused by sunbeams reflecting onceinside falling raindrops. It's the bow you usually see. The less-bright outer rainbow is the secondary bow, caused by sunbeams reflecting twice inside raindrops. Secondary bows often go unnoticed, because they are usually very faint, but they are always there.  

In Osiak's case, "you couldn't miss it," she says. Bright sunlight lancing through the clearing clouds struck droplet-laden air behind the retreating storm, resulting in an unusually intense secondary bow.   

Bron: http://spaceweather.com/