Thursday, 18 April 2013

Why is the rainbow flat? Now I know

The rainbow spanning the Great Orme to Conwy, as I was driving east along the A55 Expressway at Penmaenmawr, was strangely flat. My memory says that rainbows are big hoops, maybe twice as wide as tall, but certainly tall. So why was this so flat and low relative to the spread? I’ve Googled and read but am none the wiser. Could it have anything to do with the very strong winds blowing it over? The time was 4:30pm on 17th April.

Thank you to Ed Green for explaining. At dawn or sunset a rainbow's centre, the antisolar point, is on the horizon which means the rainbow is half in the sky and therefore a semi circle. As the sun rises the centre of the bow sinks beneath the horizon so that you only see the top of the bow. Lots more fascinating stuff about rainbows on this great website:

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