Wikipedia’s entry for Helium has these lines:
The first evidence of helium was observed on August 18, 1868, as a bright yellow line with a wavelength of 587.49 nanometers in the spectrum of the chromosphere of the Sun. The line was detected by French astronomer Jules Janssen during a total solar eclipse in Guntur, India.Wikipedia entry for Helium
The source of the information is an article in the Journal of the British Astronomical Association by R K Kochhar in 1991 ( Kochhar, R. K. (1991). “French astronomers in India during the 17th – 19th centuries“. Journal of the British Astronomical Association. 101 (2): 95–100)
The article is also a study of the work done in India by the French at the dawn of the field of astrophysics in the middle of the 19th century. Pierre Jules Cesar Janssen (1824 – 1907) had come to India to observe the total solar eclipse on August 18, 1868. Gustav Kirchoff’s work on using the solar spectrum to understand the chemical composition of the Sun was applied using a spectroscope.
The spectrometer separates elements of the electromagnetic spectrum and identifies elements by matching the spectrum to the wavelength of each element.
During the eclipse, Janssen was observing the solar prominence. These are gases that are blown off the Sun but still connected to the Sun’s surface. While studying these gases with a spectroscope, Janssen observed hydrogen gas but also observed light in another spectrum which did not correspond to any known element at the time. The observed spectrum was so bright, in fact, that Janssen thought that he did not have to wait for an eclipse to observe them again.
He was stationed at Guntoor from August 18 to September 4 when he observed the same spectral line each day. To continue studying the Sun on a daily basis, he built an instrument called a spectrohelioscope that he used to observe the Sun from Shimla.
His spectrohelioscope was used by other observers till 1891 when it was superseded by a spectroheliograph. Edward Frankland named this new element Helium after Helios, the Greek word for the Sun. When Janssen returned to France, he became Director of a new astrophysical observatory that the French government had built in Meudon, on the outskirts of Paris. He was President of the French Astronomical Society from 1895 to 1897.