Repeating the Experiment that Made Einstein Famous


A successful measurement of the solar deflection of stars during the August 21, 2017 total solar eclipse to the highest precision ever realized.


In 1919, shortly after Einstein’s theory of General Relativity predicted a very small effect, teams of scientists attempted to measure this effect during an eclipse seen in Africa and Brazil.  The results made front-page headlines and catapulted Einstein to world-wide fame.  The experiment is very difficult, and even after additional attempts as recently as 1973, the eclipse results have never been better than about 6%. With modern technology (an NP101is telescope provided by Tele Vue, a Microline ML8051CCD camera provided by Finger Lakes, and a tripod provided by Software Bisque), this historic experiment was repeated without an army of workers moving 6 tons of equipment to another continent.  With astrometric advice from the US Naval Observatory and careful preparation, I set up in Wyoming to perform this experiment, the most difficult challenge of my career. I completed the experiment with a precision of 3%. 


Results: Perfect focus, perfect exposures, perfect timing, perfect tracking, no wind, no clouds, excellent seeing.  For the first time since 1919, everything worked as planned!


May 14, 2018:  The analysis is completed and published in Classical and Quantum Gravity.  Result: L = 1.7512, in perfect agreement with the theoretical value. 



(Left) Don and Carol, next to equipment on custom base built by Steve Lang.  (Center) My measured deflections, scaled 800x. (Right) Deflections Measured in1922, scaled 2250x.



Commercial equipment today is better than ever!


The best available star catalog was used for star positions.  Corrections for optical distortion and atmospheric refraction were better than 0.01 arcsec.  During totality, I had 20 measurable stars down to magnitude 10.  Reference images, taken near the sun during totality, were used for precise calibration.  Preliminary test runs performed during twilight in April 2016 and April 2017 accurately simulated the sky con­ditions during totality, providing an accurate estimate of the final uncertainty and a good set of practice images.


Data Analysis of Eclipse Images


December 23, 2017

By subtracting a blurred corona from each of the 34 images (0.62 second exposures), then combining all of them with a small translation, 18 very accurate, but dim, stars are measureable.  Combining the 11 shorter images (0.09 seconds) allowed me to measure the two stars that are closer to the sun, and used other stars in those images to get a good alignment.  A total of 20 stars are included in my final results.  The left figure shows the image with the 0.62 sec exposures, the center figure shows the star positions indicated with the white circles, and the right figure shows the image with 0.09 sec exposure.  Based on the location of the two close-in stars, the exposures were just about perfect!




I was originally hoping to see 8 stars that would be bright enough to get good data (Eddington based his analysis on only 5 stars in 1919!).  The data shows me many more stars, so my final results were much better. (Click here to see Mathcad program example.)



Presentations and publications:


Society for Astronomical Sciences, paper and lecture, completed June 2016.

Sky & Telescope Magazine, article published August 2016.

Sky & Telescope Magazine special Eclipse issue, August 2017.

Reference to the S&T article

Reference to the S&T article

Sky & Telescope News blog

“Using Arago’s spot to monitor optical axis shift in a Petzval refractor”, D.G. Bruns, Applied Optics Vol. 56, #8, pp. 2074-2077 (2017).

“Astrometric distortion calibration of a portable refractor”, D.G. Bruns and C.T. Bruns, Applied Optics Vol. 56, #8, pp. 6288-6292 (2017).

Discover Magazine blog, interview posted May 5, 2017

Astronomy Magazine list of cool experiments, posted May 15, 2017.

Article in Live Science blog, July 26, 2017;

NASA blog

Universe of Learning: A presentation from Sonoma State

Tele Vue Optics, one of my sponsors, has been posting my progress on their own web pages.  Click here to read their stories about me:

Hackaday blog, August 16, 2017

Presentation at AstroCON, August 17, 2017, in Casper, WY. About 400 amateur astronomers in the audience.

Repeat presentation on August 18 at the Lion’s Camp for interested students and astronomers.

Setting up on Casper Mountain, video by Canon

SHSU Student blog

Newsweek mentions the experiment

Astronomy blog posted after the eclipse

Story in the Colorado Springs Gazette-Telegraph Newspaper about me and my brother getting ready for the eclipse, performing this experiment and one other

Final paper in draft form (with small errors to be corrected in the final published paper) is available at

Classical and Quantum Gravity blog

Just Science blog

CloudyNights forum

AAS blog

Inside Science blog

Very nice Tele Vue blog from NEAF, with lots of photos.

NEAF Review

NEAF talk, April 21, 2018 raw version before editing.  See Day 1, third talk. About 500 amateur astronomers in the audience.

Cosmic Perspective Radio interview by Andy Poniros at NEAF on WPKN radio 89.5FM

Final eclipse report, 2018, published by Classical and Quantum Gravity, on March 6, 2018 (Vol 35, No. 7, 12 April 2018).

Follow-up article in Sky & Telescope magazine in August 2018, and on their web page at

“Sky brightness and color measurements during the 21 August 2017 total solar eclipse”, D.G. Bruns and R. D. Bruns, Applied Optics Vol. 57 #16, pp. 4590-4594 (2018).

Astro-Imaging Channel on YouTube, discussion of my experiment by Bob Denny, author of one of the software packages I used.  He talks about my experiment for 7 minutes.

A German astronomy web blog, with an article in the September 2018 print issue.

Physics Today had a 1-year anniversary summary of Eddington’s experiment, featuring my results.

Science News had a 1-year anniversary summary of Eddington’s experiment, a shorter version of the Physics Today blog.

Discussed in an interview by Prof. Duncan (CU-Boulder) on Colorado Public Radio.

Included in “Theory and Experiment in Gravitational Physics” (Second Edition), a book by Clifford Will, published in 2018.

Invited lecture at the American Association of Physics Teachers conference in Houston in January 2019. About 100 physics teachers in the audience.

Invited lecture at the American Physical Society conference in Denver in April 2019.  About 150 physicists in the audience, including Kip Thorne (Nobel winner 2017). The slides can be seen here.

Very nice review of the APS Denver talk on the Forbes weblog, “One Hundred Years of Gravity Bending Light,” by Chad Orzel.

Smithsonian weblog on the centennial of Eddington’s success includes details of my measurements.

This Naked Scientists web article was published on the anniversary of the 1919 eclipse.

Tele Vue web blog celebrating the Centennial of the Eddington eclipse.

Sky and Telescope mentions my experiment as an example of astronomy using small telescopes, in the August 2019 issue, page 25.

Included in O Eclipse de Einstein [Einstein’s eclipse], a book by Prof. Nuno Crato and Prof. Luís Tirapicos, published in June of 2019 in Portugal. Photo by Steve Lang and a few pages of text, both in Portuguese and English.

A very complimentary article with detailed connections to Einstein, using several of my images, was published in German in a popular science magazine “Bild der Wissenschaft” (Image of Science), December 2019. The front cover has the line (translated) “Amateur researcher proves Einstein’s Theory of Relativity”. The article is titled “Der krumme Einstein-Beweis”.

Included in “A Century of Light-Bending Measurements: Bringing Solar Eclipses into the Classroom”, by Emanuele Goldoni and Ledo Stefanini, June 2020 Physics Education 55(4):045009.  A preliminary version is posted at The final version is at

Included in an article by James Overduin, Kelsey Glazer, Keri McClelland, Amelia Genus, and Chris Miskiewicz, “Solar Eclipses as a Teaching Opportunity in Relativity,” The Physics Educator, Vol. 2, No. 2 (2020). A particularly interesting passage about my results reads “This is twice the precision of the best previous professional measurements using ground-based optical telescopes (in the 1970s), and has now become part of the lore of scientific tests of general relativity.” (Thank you, James!)

WRAL in North Carolina published a three-year anniversary article about the 2017 eclipse, including a reference to my experiment.

Reason to Believe posted an article “Mastering Eddington’s Confirmation of General Relativityliv” by Jeff Zweerink, August 31, 2018.

Just Learning talks about the upcoming eclipse in 2017.

Shadow of the Moon and general relativity: Einstein, Dyson, Eddington and the 1919 light deflection in Rev. Bras. Ensino Fís. vol.41  supl.1 São Paulo  2019  Epub Dec 13, 2019

Corey Bruns lecture: Measuring Starlight Deflection During the 2017 Eclipse: Completing the Experiment that Made Einstein Famous.

Relativistic Deflection of Light Near the Sun Using Radio Signals and Visible Light, P. Marmet and C. Couture

The German popular science magazine “Bild der Wissenschaft” (Image of Science), May 2021 had a follow-up article on my unsuccessful attempt to measure starlight deflection during the daytime, “In the Shadow of the Sun”.

The German popular science magazine “Bild der Wissenschaft” (Image of Science), September 2021 had another follow-up article on my ongoing attempt to measure starlight deflection caused by Jupiter, “Solar System Test Case”.

Included in Japanese book on eclipses – to be published summer 2023.


Still to come:



Possible mention in IMAX Einstein documentary movie 2019 (release may be delayed until 2023).




Al Nagler, Tele Vue Optics, Inc., for loan of the NP101is telescope and optical raytracing.

Greg Terrance, Finger Lakes Instrumentation LLC, for loan of the ML8051 CCD camera.

Stephen Bisque, Software Bisque, Inc., for loan of the MyT Paramount tripod.

George Kaplan and John Bangert, both formerly of USNO, for astrometric advice and help with NOVAS.

Norbert Zacharias, USNO, for astrometric advice.

This research has made use of FORTRAN version of NOVAS, the Naval Observatory Vector Astrometry Software package.

This research has made use of the VizieR catalogue access tool, CDS, Strasbourg, France. The original description of the VizieR service was published in A&AS 143, 23.

Suresh Rajgopal, for help in setting up gfortran.

Corey Bruns, for help in automating the data analysis with linear algebra advice.

Ted Pecoraro, for help in improving the Paramount field tripod feet.

Steve Lang, for help setting up in Wyoming.

Jerry Kassebaum, for suggesting locations near Casper.

Greg Kinne, for help in scripting TheSky.

Ron Bruns, for calibrating weather instruments and operating an auxiliary experiment.


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Web page last updated March 1, 2023.