Remember being amazed by rainbows?  Wondering how they formed? Wanting to find the end of the rainbow and the elusive pot of gold? From cereal boxes, to YouTube Viral videos, to bagels, rainbows continue to delight us.  But how are rainbows formed and how did it they become associated with Leprechauns?

The Answer to how lies in the physics of refraction and Snell’s Law.   Snell’s law relates the angles of incidence and refraction of a light ray to the density of two different materials.  As light passes from a medium of low density to a medium of higher density, or vice versa, the light ray bends. How far it bends depends on wavelength.  Different wavelengths bend at different angles, physicists call this dispersion.  Visual light consists of wavelengths from 400-700 nm, red to violet.   When the air is filled with water droplets light hits the drops and is refracted, bent, within the droplet.  The droplet separates the white light into a spectrum of colors.  Since water droplets are spherical the light emerges in a circle.  Rainbows can only be seen when the sun is to our backs and when we are at a viewing angle of 40-42 degrees.  When the conditions are right and we are lucky enough to be standing in the right position we see a rainbow.

How the rainbow became associated with leprechauns is not so simple.  Leprechauns as we know them today evolved from stories of trickster faeries in Ireland.  Well known in popular culture and mythology as small men the terms Leprechaun comes from the words “small body”.  According to mythology the connection between leprechauns and rainbows grew from Viking invaders wanting to find the burial gold of the local people, who they called the little people for their small stature. Unable to find the mounds with gold legend slowly grew up linking the elusive rainbow with the elusive gold treasure.  As time passed the small people became leprechauns and the burial mounds turned into the pot of gold at the end of the rainbow.

Myths

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Maths

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