Measuring Gravitational Deflections is Really Hard

Between 1922 and 2017, astronomers had some great opportunities to measure the gravitational deflection of starlight by observing the Sun during a total eclipse. The 1922 eclipse gave good results, but bad weather or equipment problems plagued many of the later expeditions. Starting in the 1970s, radio telescope measurements yielded much better results, generally reducing the interest in optical measurements. Orbiting optical observatories gave nearly perfect values starting in the 1990s. However, the interest in repeating Eddington’s experiment was revived in 2017, probably due to the convenience of the total eclipse that passed over the USA. While at least nine amateur astronomers or teams set up to repeat this experiment, most of them still had problems with weather or equipment. This talk will discuss the difficulties experienced since 1922, and how the combination of good weather, amateur equipment, and careful planning resulted in the best deflection values ever measured during a solar eclipse.