MadSci Network: Physics

Re: I was taught that the colors of the rainbow match ROY G BIV.

Area: Physics
Posted By: Dacian Bonta, Grad student in Medical Physics, University of Chicago
Date: Mon Jan 13 15:05:53 1997
Message ID: 852976028.Ph

The rainbow is one of the most beautiful things in nature. The theory which explains the rainbow was proposed almost four centuries ago by the great french philosopher and scientist DESCARTES.

Light propagates differently through various media in the respect that its speed differs from air to water for example. Also the yellow light propagates with lower speed in water than blue light. The difference in speed makes the different colours to be deviated differently when passing through water. That's why the rainbow which is due to light transmission and reflection in rain drops has all the colours and not only one color the color of sunlight. What have you seen may have two explanations:

1. You have seen the second rainbow ( there is a second rainbow inside the first one with the colors inverted: instead of ROYGBIV this second rainbow is VIBGYOR) so you could see yellow under violet. This second rainbow is less intense than the first one but in special conditions (clear sky, impossibility to see the first rainbow) it can be seen. You have to be aware that the rainbow originates in a big volume of the sky by the sunlight reflecting and transmitting trough huge numbers of raindrops. Thats why a big number of phenomena are possible.

2. The second possibility is that you have seen the direct reflection of sunlight in the ice drops. Because it is very cold up there the raindrops can freeze on their way down and melt again when approaching the ground. This would explain the strong yellow band of light you saw. In this case this band originated in a different area of the sky than the rainbow but came under a similar angle with the rainbow so they seemed close.

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