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The full spectrum

13 Apr 2014, 00:00 UTC
The full spectrum
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The astronomer famous for discovering Uranus also discovered something he couldn't see. By accident, he took its temperature. Continue reading →

¡SkyCaramba! weekly astronomy blog for the week ending April 19, 2014
The astronomer famous for discovering Uranus also discovered something he couldn’t see. By accident, he took its temperature.
In 1800, William Herschel used filters of various colors to observe the sun. He found that a red filter let a lot of heat through. Wondering if different colors have different temperatures, he set up a prism to let the sun shine through and he placed thermometers in the color band on the other side. Indeed, the different colors did have different temperatures. The thermometers raised to different levels. The closer they were to the red end, the higher they climbed.
Familiar with scientific practices, Herschel also used one or two control thermometers placed away from the spectrum. With no sunlight shining on them, Herschel could make sure the sun and not something else in the room caused the temperature changes. What happened when he put a control thermometer near the spectrum, but not in it, surprised him.
Until then, the thermometer placed in the red light had registered the ...

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