Pierre Janssen

Pierre Jules César Janssen (22 February 1824 – 23 December 1907), usually known as Jules Janssen, was a French astronomer who, along with English scientist Joseph Norman Lockyer, is credited with discovering the gaseous nature of the solar chromosphere, and with some justification the element helium.

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Astronomer Pierre Janssen was he first to regularly use photographs to study the Sun. In 1903 he published his great "Atlas de photographies solaires", containing more than 6,000 solar pictures

In 1868 Pierre Janssen watched the moon pass in front of the Sun. Using a special prism, he became obsessed with a line of yellow light that everyone assumed was sodium so he kept studying that mysterious line. Joseph Lockyer worked on the same problem and both are credited for helium