Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: chris on 16/01/2008 23:27:40
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What governs the shape of a rainbow? Is it actually circular if you look at it from the correct position?
Chris
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I do believe it is the combination of the many roundish rain drops through which the light is refracted into the different colors, the position of the sun and the curvature of the earth. Together, the rays of the sun get bent into a curve.
A more accurate scientific explanation will be forthcoming I am sure but, what the heck, I can try can't I?
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Having to do with light bending eh? I think!
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A rainbow is always circular (or a part of a circle). This is because the light is reflected internally on the inside of spherical water droplets. Because of dispersion, the various colours (wavelengths) are refracted (bent) a bit differently as they enter and leave the drops. The light comes from the Sun and, any ray that enters your eye will always have been bent by the same amount (i.e. the same angle). Remember, the Sun is behind you and the bow will be in front of you. The symmetry of the situation means that there will be a cone of light (constant angle) of each particular wavelength entering your eye so you will see a circle.
Have a look at this:
http://eo.ucar.edu/rainbows/ (http://eo.ucar.edu/rainbows/)
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"Is it actually circular if you look at it from the correct position?"
A 22 degree rainbow, or halo, will be a complete, visable, full circle viewed from the ground. The colours will be less spectacular...but you do get the full circle.
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Complete rainbow circles are visible from aircraft ...
http://www.atoptics.co.uk/droplets/gloim21.htm
Or mountain tops ...
http://www.atoptics.co.uk/droplets/gloim20.htm