WHY DOES A RAINBOW APPEAR CURVED?
AND HOW WOULD IT APPEAR FROM AN AEROPLANE( CIRCULAR?) AND WHY?
is it cause the way the sun is shining and the angle the light is split?
Rainbows are coloured because water droplets are like prisms, and it appears curved because of the angle at which you see it. For a proper explanation, check here:
Refraction and the Rainbow
The rainbow is an arc of what would ideally be a full circle which surrounds the anti-solar point (the point exactly opposite to the sun in the sky - below the horizon of course during the daytime). In actual cases you usually only see a fragment of the whole circle, but it is still a circular arc, and that's why it's curved.
Sunlight is double refracted in a drop of water in a cloud. It is refracted going into the drop, is then internally reflected back and refracts again going out. This spreads the colors out more than a single refraction would. The dispersed beam then heads back roughly in the direction it came, that is toward the sun. If you want to see the rainbow you have to turn your back on the sun. IIRC the radius of the arc circle is 47.5o.
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