Alaska-sized Rainbows Sprout on the Last Frontier
Not only is Alaska the best spot in America to hook a king salmon, see the Northern Lights, catch a midnight sun tan and study mosquitoes, the state also happens to be one of the most fertile breeding grounds for rainbows.
Spotty summertime afternoon and evening rains in Alaska make for perfect rainbow conditions when coupled with the fact that our position on the earth causes the sun to hover just above the horizon for a long time here. Rainbows are tallest and most vivid when the sun is at a low angle, as is so often the case in Alaska.
Rainbows form when the sun is shining in one part of the sky, it's raining in another, and the rainbow-seer is somewhere in between, with his or her back to the sun. According to Jerry Dennis, in his book It's Raining Frogs and Fishes, individual rain drops act together to separate the light of the sun into the reds, yellows, oranges, greens, blues and violets we see as the colors of a rainbow.
The show begins when sunlight from over the rainbow-viewer's shoulder strikes tiny, globe-shaped raindrops from a shower on the horizon. The raindrops act as little prisms, dividing the white or yellow light we normally see into the visible spectrum of colors. Raindrops sort out light rays by color because each frequency of light bends at a different angle when it enters the liquid shell of the drop. The different colors of light strike the back wall of a raindrop at slightly different angles and boomerang back to our eyes, so we see different colors from different raindrops.
The rainbow we see is the product of millions of drops, with bunches of them reflecting reds, yellows and so on to form the complete arch. This bow, however, is only half the image of a colorful circle. The bulls-eye of this circle, called the anti-solar point, lies as far below the horizon as the sun is above the horizon at our backs. Therefore, when the sun is low over the horizon, the center of the rainbow circle is closer to the ground surface, and we see a tall, Alaska-sized rainbow. From an airplane, it's possible to see the complete ring of a rainbow if you happen to by flying above rain-filled clouds that have a high sun shining on them.
Many people have seen a faint rainbow riding piggyback above a bright rainbow. This "secondary" rainbow is formed from high raindrops that reflect rainbow colors twice before they reach our eyes, as opposed to once. This extra reflection absorbs some of the light's energy, so the rainbow appears washed out. Because of the double reflection, the colors of the rainbow are also reversed, with red closest to the ground and purple facing the sky.
A nice feature about rainbows is they are exclusively the beholder's. Because only one ray of light enters the eye from each raindrop, a different rainbow is seen from every angle. Thus, the little girl on her father's shoulders doesn't see the exact rainbow her dad sees. And attempts to bask in the earth-touching color of a rainbow will end in frustration, because walking toward a rainbow will eventually mess up the angle at which a rainbow's light reaches the eye, causing the rainbow to disappear. Sigh.
