Light Times Two – a poem by Kate Rauner
The speed of light is constant,
That’s what you think you know.
But only in a vacuum.
Through glass it can go slow.
An index of refraction
Predicts the speed of light,
Determines how the wave is bent
On its transverse flight.
Some light transmits through the glass,
And some will be reflected.
Brewster’s angles, Fresnel calcs,
The focal length of lenses.
So with great precision,
With science as explainer,
Every light on my Christmas tree,
In the window, has a doppelganger.
Optics is a fascinating field. Consider the refractive index at wikipedia.