- 1851
The first photograph of totality
On 28 July 1851, at the Royal Prussian Observatory in Königsberg, the daguerreotypist Johann Julius Friedrich Berkowski exposed a silver-coated plate for 84 seconds through a small refracting telescope. It was the first successful photograph of a total solar eclipse.
- 1860
Prominences belong to the Sun
On 18 July 1860, Warren De la Rue photographed the eclipse from Rivabellosa in northern Spain, while the Jesuit astronomer Angelo Secchi photographed it from a site several hundred kilometres to the south. The red prominences matched in both sets of pictures, so they could not be an effect of the Earth’s atmosphere or the Moon: they were part of the Sun.
- 1868
Helium is discovered in the Sun
During the eclipse of 18 August 1868, Jules Janssen, observing from Guntur in India, saw a bright yellow line at 587.49 nanometres in the light from the edge of the Sun. Two months later Norman Lockyer observed the same line and concluded that it came from an unknown element, which he and the chemist Edward Frankland named helium, after helios, the Greek word for the Sun. It was isolated on Earth in 1895.
- 1869
The mystery of coronium
At the eclipse of 7 August 1869, Charles Young and William Harkness independently recorded a green line in the spectrum of the corona that matched no known element. It was put down to a new element called coronium. In the 1930s Walter Grotrian and Bengt Edlén showed it came from iron that had lost thirteen electrons, which can only happen at extreme temperatures. The corona turned out to be far hotter than the Sun’s surface.
- 1919
Starlight bends around the Sun
On 29 May 1919, Arthur Eddington observed from the island of Príncipe off West Africa, while Charles Davidson and Andrew Crommelin observed from Sobral in north-east Brazil. They measured the positions of stars near the eclipsed Sun and compared them with photographs taken months earlier. The stars appeared shifted, as Einstein’s general theory of relativity predicted, and the results were announced to the Royal Society and the Royal Astronomical Society on 6 November 1919.
- 1973
74 minutes under the shadow
On 30 June 1973, a prototype Concorde, 001, took off from Las Palmas in the Canary Islands with a team of scientists and their instruments on board. Flying at about Mach 2 and 18,000 metres, it kept pace with the Moon’s shadow across Africa and gave scientists 74 minutes of totality, far longer than any observer on the ground has ever had.
Why eclipses still matter
Instruments called coronagraphs can now block the Sun artificially, and spacecraft watch the corona constantly. But a total eclipse still gives the clearest view of the inner corona, close to the Sun’s edge, which is exactly where the questions of how the corona is heated and how the solar wind is launched are decided. That is why research teams still travel to every total eclipse, including the long one on 2 August 2027.