All material, when hot, will emit light. Everyday examples abound: the stove element in the kitchen, the metal filament in a lightbulb, and even the Sun.

By the end of the 1800’s, scientists were observing this phenomenon in their laboratories but could not explain it. Despite this lack of understanding, they nonetheless knew how to separate the light emitted by a gas into a spectrum that was diagnostic of the chemical elements contained in the gas. In 1859, the German physicist Gustav Robert Kirchhoff called this type of spectrum an “emission spectrum”.

Many researchers attempted to explain how matter could generate an emission spectrum but without success. It was only in 1900 that the German physicist Max Planck would provide part of the answer.

Planck noted that it was impossible to solve the problem using existing principles of physics and proceeded to develop a revolutionary theory that marked nothing less than the beginning of modern physics.

In his theory, Planck maintained that light could only be emitted as small packets of energy that he named “quanta” (later known as “photons”). This proposal ran contrary to all contemporary knowledge about light at that time.

In fact, light was considered to be a continuous form of energy that propagated as an electromagnetic wave and not – as Planck proposed – as a form of discontinous energy in the form of particles, like photons.
ASTROLab of Mont-Mégantic National Park

© 2006 An original idea and a realization of the ASTROLab of Mont-Mégantic National Park

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