Photography and Eclipse Observations.

Since the middle of the nineteenth century solar eclipses had attracted intense interest among astronomers. The invention of photography and its application to astronomical observations made it possible to record with great precision the solar phenomena that eclipses revealed. Although some primitive daguerreotype photographs had been made of both the sun and the moon in the 1840s, the crucial breakthrough came with Englishman Warren de la Rue's invention of the photoheliograph, a photographic telescope with a fast shutter that could be used to map the surface of the sun.

Solar Prominences.

The first significant riddle that astronomical photography resolved concerned the existence of solar prominences, protuberances from the sun's outer edge that had long puzzled astronomers. It was not clear whether they were physical features of the sun or merely optical illusions. De la Rue took his photoheliograph to...