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| Zero order glow formation |  |
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Most of the sunlight entering raindrops leaves the other side without internal reflection. Only a small fraction is reflected to form the primary, secondary and higher order rainbows - in the diagram these rainbow forming rays are shown very faint. | No
internal reflection |
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| As
the distance of the incident ray from the drop centre increases,
the outgoing ray deviation increases continuously . There
is no
turning point or angle of minimum deviation
at each side of which the deflection changes in the same direction.
This is why the zero order rays do not produce a rainbow. |
No turning point, no rainbow | ||
| Contrast the zero order behaviour with that of the primary bow rays. In the latter the deflection decreases to a minimum - the rainbow angle - and then starts to increase again as the incident ray's distance from the drop centre is continuously increased. | Different behaviour from rainbow rays | ||
| Refraction
disperses the colours but they overlap again outside the drop. The
glow is the same colour as the incident sunlight. |
Colours recombine | ||
| The
brightness of the zero order glow is one of the causes of the difficulty
in ever seeing 3rd and 4th order rainbows
outdoors. |
Bright sky inside the bow |