This week’s solar eclipse has captured the imaginations of astronomers and the general public alike, not least because it will be the last opportunity to witness such an event for over a decade. To further add to its rarity value, although we in Britain can observe a partial eclipse, the total solar eclipse will only be visible from the remote locations of the Faroe Islands and Svalbard. The Faroe Islands naturally intend to follow this with ‘major celebrations’.
Solar eclipses have, of course, long been an object of interest for Fellows of the Royal Society. Robert Hooke recorded his observations of 22 June 1666 in his ‘Account of the Eclipse of the Sun’, as observed for a duration of one hour and 54 minutes by Francis Willughby, Dr Pope, Mr Phillips and Hooke at Gresham College (RBO/3/49):
‘Wee observed the figure of this Eclipse, and measured the Digits, by casting the figure through a five-foot Telescope on an extended paper fix’d at a certain distance from the eye-glasse…’
Techniques of observing eclipses became a significant driver for scientific enquiry. In the Victorian era, for example, Norman Lockyer (1836–1920) was one of a group of interested Fellows developing the relatively new science of astrophysics to great effect. While discussing the American Eclipse of 1869 (first reported to the Society in volume 18 of its Proceedings journal), Lockyer evocatively described the reason for astronomers’ interest:
‘It is only when hid in dire eclipse that our feeble human eye can appreciate all the wonders of our great light-giver … An eclipse of the sun, so beautiful, and yet so terrible to the mass of mankind, is of especial value to the astronomer, because at such times the dark body of the moon, far outside our atmosphere, cuts off the sun’s light from it, and round the place occupied by the moon and moon-eclipsed sun there is therefore none of the glare which we usually see – a glare caused by the reflection of the sun’s light in our atmosphere’. (Contributions to Solar Physics by J Norman Lockyer, London, 1874, p.104 and p.240).
The French astronomer Jules Janssen observed a bright line in the spectrum of the Sun’s chromosphere when viewing the 18 August 1868 total solar eclipse from Madras in India. Realising that the spectral line was bright enough to observe in the absence of an eclipse – useful given the infrequent nature of the phenomenon – Janssen made further measurements, as did Lockyer that October using a powerful new spectroscope at his home in West Hampstead. Lockyer’s spectroscope, he reports, was improved through funds granted by the Royal Society Government Grant Committee in 1867, though delays meant that he was unable to test it until the following year.
The bright line within the spectrum of the chromosphere was identified through Janssen’s and Lockyer’s observations as the previously unknown element ‘helium’, though this was not isolated on Earth until William Ramsay‘s laboratory research in the 1890s. Janssen and Lockyer’s independent and near-simultaneous spectroscopic innovations in observing the chromosphere and solar prominences were recognised by a joint medal cast in 1872 by the French Académie des Sciences.
Scientific interest in observing eclipses continued – Lockyer, for instance, was in charge of the Sicilian party of the Mediterranean Eclipse expedition of 1870, and the Royal Society supported the expedition of 1871 to witness the eclipse in India and Sri Lanka. There are of course many further examples, such as the 1886 expedition to Grenada, composed of a team including Lockyer, Captain Leonard Darwin, Thomas Edward Thorpe and Dr Arthur Schuster; and preparations for the 1896 eclipse, with Michael Foster writing a letter on 20 January 1894 to the Secretary of the Royal Astronomical Society to propose collaborative action (NLB/8/902 – a letter recently catalogued as part of our ongoing initiative to open up the New Letter Books).
So, whether you observe it through a pinhole projector, reflected in a bucket of water, or via a more sophisticated device, we hope that you will all share the enthusiasm of Robert Hooke, Norman Lockyer and their colleagues when witnessing the March 2015 eclipse!