Eclipse observation. Engraving of astronomers observing a total solar eclipse in 1869. A man is changing a photographic plate in the largest telescope. This Canadian team observed a total solar eclipse in Iowa, USA. They made an early use of astronomical photography and spectroscopy, and proved that the corona originates in the Sun. The corona is the Sun's outer atmosphere and is impossible to observe except during an eclipse because of the luminosity of the solar disc and the sun-induced brightening of the earth's atmosphere.