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Bright Subject

April 2, 2020

Until 1845, almost no one had seen the Sun as anything other than a bright disk in the daytime sky. A few astronomers had looked at it with special telescopes, or traced its projected image on a piece of paper. But that was about it.

Fizeau and Foucault 1845 Daguerreotype of the SunThat changed 175 years ago today, when two French scientists snapped the first large photograph of the Sun. It was published in a book about astronomy, and later in other places — giving the world a close-up look at our star.

Armand Fizeau and Leon Foucault were young scientists fresh out of college. They were interested in the daguerreotype process — the first successful technique for taking photographs. It involved coating a copper plate with light-sensitive chemicals, exposing the plate, then using other chemicals to reveal the image.

Fizeau and Foucault refined the technique, then snapped a series of pictures of the Sun. Those images were tiny, though — the Sun was only about half an inch across — so they revealed almost no detail.

But on April 2nd of 1845, they took a much larger picture — the Sun measured about four and a half inches across. It showed two groups of sunspots, as well as some of the “bumpiness” on the Sun’s surface.

Fizeau and Foucault each spent a lot more time studying the Sun. And each of them used their observations to calculate the speed of light. They came up with numbers that were within a few percent of the true value — all from watching the Sun.


Script by Damond Benningfield

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