Sorry Chief, I’m unaware of any special significance of the numeral 37.5, particularly in reference to rainbows.
With reference to the age of people; I'd consider it a pretty "low" number.
The refractive angle, for a rainbow, is the angle between the light ray that enters a rain droplet and the light ray leaving that droplet. This angle determines the angle at which the top of the rainbow appears in the sky; that angle being the difference between the refractive angle and the elevation angle of the sun in the sky.
“Snell’s Law” describes the relationship between the angles at which light enters and leaves a boundary between materials with different indices of refraction.
➥ Refraction and Snell's Law
The folloqwing Q&A is Excerpted from
➥ Frequently Asked Questions about Rainbows
Q. How is a rainbow formed?
You need a few things to see a rainbow. The main things are rain, you need that rain to be illuminated by bright sunshine, and the rain must be in the right position relative to you. A primary rainbow is always somewhere on an arc
42 degrees around the shadow of your head
(called the anti solar
point). So the brightly illuminated rain must be in this direction away from you to see a rainbow. For a secondary bow it is 51 degrees around the shadow of your head
A rainbow is caused by the refraction and internal reflection of light inside rain drops, which results in the white sunlight being separated out into the colours of the rainbow. See the detailed pages which are linked to at the top of this page for a more in depth
Q. What is the shape of a rainbow?
Rainbows are an arc
at a constant angle from the anti solar
point (shadow of your head). For a primary bow this angle is 42 degrees, and for a secondary bow 51 degrees. So the shape is an arc along the circumference of a circle.