The eclipse that proved a coup for Newtonian theory

300 years ago, on 3 May 1715, a rare solar eclipse occurred over England. It was the first to be predicted on the basis of the Newtonian theory of universal gravitation, its path forecast – accurately – in advance.

The Observer has fascinating piece looking at this landmark day for science.

The eclipse is known as Halley’s Eclipse, after Edmond Halley, who produced accurate predictions of its timing and an easily-read map of the eclipse’s path. Halley did not live to see the confirmation of his predictions of a returning comet – a 1759 triumph for the Newtonian system – but he was able to enjoy his 1715 calculations, which were within 4 minutes, and to improve on them with a corrected map (above). He observed the eclipse from the Royal Society’s building in Crane Court on a morning with a sky of “perfect serene azure blew”.

Halley used his map of the eclipses path to promote the successes of science, writing

The like Eclipse having not for many ages been seen in the Southern Parts of Great Britain, I thought it not improper to give the Publick an Account thereof, that the sudden darkness, wherein the Starrs will be visible about the Sun, may give no surprize to the People, who would, if unadvertized, be apt to look upon it as Ominous, and to interpret it as portending evill to our Sovereign Lord King George and his Government, which God preserve. Hereby they will see that there is nothing in it more than Natural, and no more than the necessary result of the Motions of the Sun and Moon; And how well those are understood will appear by this Eclipse.

But while the eclipse prediction was the first to use Newtonian principles, it was far from the first prediction.

Eclipses have been predicted since ancient times, although usually lunar rather than solar. The former (where the Earth’s shadow comes between the Sun and the Moon, rather than the Moon passing between the Earth and the Sun) are much more frequent and less complicated to calculate. Predicting solar eclipses accurately requires understanding of the fiendishly complex motion of the Moon – and seeing them requires a lot of patience.


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