Measuring Starlight Deflection during the 2017 Eclipse: Repeating the Experiment that made Einstein Famous

Dr. Don Bruns

In 1919, astronomers performed an experiment during a solar eclipse, attempting to measure the deflection of stars near the sun, in order to verify Einstein’s theory of general relativity.  The experiment was very difficult and the results were marginal, but the success made Albert Einstein famous around the world.  Astronomers last repeated the experiment in 1973, achieving an error of 11%.  On August 21, 2017, using amateur equipment and modern technology, I plan to repeat the experiment and achieve a 1% error.  The best available star catalog will be used for star positions.  Corrections for optical distortion and atmospheric refraction are better than 0.01 arcsec.  During totality, I expect 7 or 8 measurable stars down to magnitude 9.5, based on analysis of previous eclipse measurements taken by amateurs.  Reference images, taken near the sun during totality, will be used for precise calibration.  Preliminary test runs performed during twilight in April 2017 accurately simulated the sky con­ditions during totality, providing an accurate estimate of the final uncertainty.


Dr Bruns has been an amateur astronomer since his first department store refractor showed the rings of Saturn and lunar craters when he was 11 years old. He has continued to explore telescopes and optics, completing his doctorate in physics from the University of Illinois in 1978. His long and varied career included work developing new lasers, thermal infrared sensors, and fiber optics instrumentation. He was especially pleased to include astronomy in his work, including designing novel adaptive optics components and high precision celestial navigation equipment. Now retired, he is interested in repeating challenging historical experiments using modern equipment.


Thursday, August 17, 2017 - 13:45