A few days ago in Östersund, Sweden, Göran Strand saw a beautiful double rainbow. The arcing colors, however, were not what attracted his attention. "The amazing thing was the dark band between them!" he says.
"This band is called Alexander's dark band after Alexander of Aphrodisias who first described the effect in 200 AD." says Strand.
All double rainbows are separated by such a band. The bright primary bow (on the left) is formed by light reflected once inside raindrops. The less-bright secondary bow (on the right) is formed by light reflected twice inside raindrops. These reflections, single vs. double, scatter light in opposite directions. In between the two rainbows, light is simply not bent toward the observer, so it looks dark.
And that's how rainbows can suck light out of the sky. Find more examples in the Realtime Rainbow Photo Gallery! www.spaceweather.com
All double rainbows are separated by such a band. The bright primary bow (on the left) is formed by light reflected once inside raindrops. The less-bright secondary bow (on the right) is formed by light reflected twice inside raindrops. These reflections, single vs. double, scatter light in opposite directions. In between the two rainbows, light is simply not bent toward the observer, so it looks dark.
And that's how rainbows can suck light out of the sky. Find more examples in the Realtime Rainbow Photo Gallery! www.spaceweather.com
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