It was predicted from Newtonian physics already in the 18th century that gravity should bend light, but not by as much as general relativity predicts. This was first confirmed during a solar eclipse in 1919. Surely, solar eclipses were imaged long before that. Didn't anyone notice that stars near the Sun were displaced? Hadn't anyone thought of testing the newtonian prediction of bent light?

  • $\begingroup$ The displacement was only 1.5 arcsec at the limb of the Sun. This was an extremely challenging measurement at the time, especially using the portable equipment available. Also, without an alternative theory, the motivation to do a difficult test of the prevailing theory, that can be tested in other ways, was weak. $\endgroup$ – Rob Jeffries Mar 26 '16 at 7:49

I suggest reading the paper on the 1919 expedition to get a clearer picture of why they did it at that time and why it hadn't been done before. From reading chapter 2 I think the main reason was the astrophotography equipment required for the experiment and the alignment of bright enough stars close to the sun to observe the effect.

Of course before Einsteins prediction in 1911 no one had any specific reason to observe the stars close to a solar eclipse before and during totality, it might seem obvious now but that's hindsight for you.

  • $\begingroup$ It is odd that in over 200 years no one thought of observing Newton's prediction that gravity bends light. $\endgroup$ – LocalFluff Mar 25 '16 at 12:38
  • $\begingroup$ It is not odd at all. You should not judge scientists of days gone by based on what scientists of today know. $\endgroup$ – David Hammen Mar 25 '16 at 13:46
  • $\begingroup$ What an awesome paper. It would never be accepted in that form today. It seems clear that what was required was a portable instrument with high precision and the motivation to use it. $\endgroup$ – Rob Jeffries Mar 26 '16 at 7:45

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