What is difference between primary rainbow and secondary rainbow ?
Rainbows are not seen in midday since the whole 42° circle is below the horizon at most latitudes. So rainbows tend to be seen most in the later afternoon when a thundershower has passed and the sun from the west is illuminating the receding edge of an eastwardly moving raincloud. It is possible to see the entire circle of the rainbow from an airplane since there can be falling droplets both above and below you.
The secondary rainbow is about 10° further out from the antisolar point than the pimary bow, is about twice as wide, and has its colors reversed.
According to Schaaf, the light of the secondary bow is one-tenth the intensity of that of the primary bow, given the same viewing conditions.
Photos by Mary Lassiter, used by permission. Note the reversal in the order of the colors in the secondary rainbow. These photos also show the increase in brightness inside the primary rainbow. The region between the two rainbows should be a bit darker than the sky just outside the secondary rainbow, but this is a smaller difference.
primary rainbow: The most common of the principal rainbow phenomena, which appears as an arc of angular radius of about 42° about the observer's antisolar point; it is the inner of two rainbows, whose light undergoes only one internal reflection, and which is narrower and brighter than the outer, or secondary, rainbow.
secondary rainbow:A faint rainbow of angular radius about 50° which may appear outside the primary rainbow of 42° radius, and which has its colors in reverse order to those of the primary. Also known as secondary bow.
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