William Herschel
The discoverer of infrared light and heat

How light becomes heat

Who was William Herschel

William Herschel's life, who was he and why is he associated with infrared heating? First a short summary of who he was and what he did.

Frederick William Herschel was born on November 15, 1738 in a family of musicians. He grew up in Germany in the Hanover region. In 1757, he fled Germany and sought a new home in England.

Here he made a living as an organist and later as a composer and conductor. It is in 1772 that his sister Caroline joined the orchestra as a singer. Both began to focus on astronomy in their spare time.

Especially building ever bigger and better telescopes became his passion. It is not until 1781 that Herschel became famous when he discovered the planet Uranus on March 13, 1781. Before this discovery, Herschel was an unknown amateur astronomer.

Measuring the movement of the sun

Herschel's work on double stars, which he pursued intermittently between 1782 and 1821, was the first demonstration that gravity also operated outside the solar system.

He also made one of the first attempts to measure the Sun's motion through the Milky Way using the motion of nearby stars.

This was yet another step in the removal of the Earth as the centre of the universe. His larger and more powerful telescopes also allowed him to solve many of the hitherto mysterious "nebulae" in clusters of faint stars.

As his sister Caroline began to focus more and more on discovering comets, William became interested in the sun.
William Herschel prisma

Temperature measurement of each unique color

In 1800, he became interested in the solar spectrum and discovered the first evidence for solar energy output outside the "visible spectrum", in what is now known as the infrared spectrum.

Thanks to the use of red filter glass, he discovered that the light produced a lot of heat. Wanting to learn more about it, he split the sunlight into different colours using a prism, so he could measure the different temperatures of each colour.

He placed different thermometers on the different light colours that came out of the prism. He also placed a thermometer outside the range of the last visible colour emerging from the prism.

William Herschel discovered that the latter thermometer measured a much higher temperature than all other thermometers in the visible colours.
He discovered that there was an invisible, heat-producing wavelength under (“infra”) the red light path. This wavelength was eventually called “InfraRed”.

Herschel's experiment was important not only because it led to the discovery of infrared, but also because it was the first time that someone had somehow demonstrated that there are forms of light that we cannot see with our eyes.

William Herschel's original prism and mirror are on display at the National Museum of Science and Industry in London. Today infrared technology has many interesting and useful applications, including infrared heating.
Infrared light

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