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Rainbow Disk imaged near sunset by Adrian Czerniak in southern Ontario, Canada on 8th June '08. ©Adrian Czerniak, shown with permission.
Rainbows are not bows, they are disks, albeit brightening towards the edge.
The primary is made by sun rays reflected once inside raindrops. Each drop deflects and spreads the rays into a range of angles. Those rays that enter our eye are seen as a glint, like the flash of a jewel. The glints from all the individual raindrops form a disk in the sky.
The disk takes the sun's colour because the coloured raindrop glints overlap and merge. Other than at sunset it looks like brighter sky.
Only at the disk edge do we see colours because the red disk is largest followed in size by those of yellow, green and blue.

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