1845: The first solar photograph

The first photographic technique was developped in 1839 [CHECK] by Niepce and Daguerre, and relied on the exposure of a thin iodine layer deposited on a silver substrate, subsequently fixed in a mercury bath. The images so produced became known as Daguerrotypes. This imaging technique was very soon applied to astronomy, through the enthusiastic support of the french astronomer and politician Francois Arago, and the british astronomer John Herschel (son of
William Herschel), who first coined the term "photography".

The first succesful Daguerrotype of the Sun, reproduced below, was made on 2 April 1845 by the physicists H. Fizeau and Leon Foucault (perhaps better known for their various pioneering measurements of the speed of light). The exposure was 1/60 of a second. This image shows the umbra/penumbra structure of sunspots, as well as limb darkening.


Reproduction of the first daguerrotype of the Sun. The original image was a little over 12 centimeters in diameter. Reproduced from G. De Vaucouleurs, Astronomical Photography, MacMillan, 1961 [plate 1].

Daguerre's photoraphic process was soon supplanted by a new technique developed starting in 1851, based on a colloidal suspension on a glass substrate. This is the direct ancestor of modern photographic film. In 1858 daily photographic record of the solar disk using a solar telescope especially designed for photography began at Kew, in England, under the leadership of Warren de la Rue