William Herschel, a famous astronomer of the mid 1700s through the early 1800s, is probably most famous for discovering the planet, Uranus, the first planet discovered with the use of a telescope.
He was messing around with prisms and sunbeams one day in the year 1800 when he noticed that the air in the red part of the spectrum seemed warmer than the other colors. Intrigued, he measured the spectrum of prism colors with a thermometer, and soon discovered that the air was actually warmest just outside the red light. He declared that there must be some sort of invisible light being refracted onto that spot and he called this light calorific from “calor,” the Latin word for heat.
We now call these rays “infrared” and we now understand that this is how heat is radiated. When the sun feels warm on your skin, you are experiencing infrared radiation from 93 million miles away. This heat, however, does not cause sunburn. Rather, it is the ultraviolet (UV) rays at the other end of the spectrum which are dangerous.