Light, Sound and Waves

Alexander’s band

Stories from Physics for 11-14 14-16 IOP RESOURCES

In around AD 200, Alexander of Aphrodisius observed that, during rain, the area between primary and secondary rainbows appears considerably darker than the surrounding sky. This area has been labelled Alexander’s band. The phenomenon occurs because the refractive index of light means that light from raindrops in the region of the sky between the two rainbows cannot reach the observer.


can be represented by Ray Diagrams
formalised by Snell's Law
has the special case Total Internal Reflection
is used in analyses relating to Lens
can be analysed using the quantity Refractive Index
can be exhibited by Progressive Wave
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