The May 29, 1919 eclipse, that happened 100-years ago this past week, will always be remembered as a key “turning point” in the history of physics. “Lights All Askew in the Heavens” exclaimed a New York Times headline while The Pittsburgh Gazette Times declared that the “Elusive ‘Fourth Dimension’ Finally Proven to Exist == Newton Theory Refuted.” Newspaper editors in 1919 were grasping at straws to explain the result of an experiment that crazily proved that star light was bent by the gravity of the Sun. Their articles on the subject introduced the names of English astronomer, Arthur Eddington, and the German scientist Albert Einstein to the public. It was Eddington that announced to the world the results of an experiment he organized to test a theory put forth by the then obscure German physicist. What made Eddington’s announcement unusual was that he was an English scientist propping up a theory from a German scientist in the acrimonious aftermath of the First World War. This was just a few months after the signing of the Treaty of Versailles.
It was Einstein’s idea to test his General Theory of Relativity (a geometric theory of gravitation) during a total solar eclipse. Einstein theorized that starlight passing by the Sun would be bent by its gravity. The eclipse would darken the sky enough to allow bright stars to be photographed near the Sun by observers on the Earth. Comparing eclipse images of these stars to images made when they were in the night-time sky (some months on either side of eclipse date) should show the difference in position. The May 29, 1919 eclipse came about at the right time to test the theory: it was the longest eclipse in 500-years (6′:51″ maximum totality) and the bright stars of the Hyades star cluster were fortuitously near the Sun. The center-line was through the heart of South American and southern Africa and expeditions were sent to Brazil and the island of Principe off the coast of Africa.
Eddington traveled to Principe to supervise the test and got photographic plates good enough to measure star positions. (The Brazil expedition had focus failure due to the heat of the Sun distorting the optics.) He found that the difference in position of the stars was just as Einstein had theorized and announced the results at a Royal Society meeting in November 1919 to world-wide acclaim.
Attempts to use an eclipse to confirm an outcome of Einstein’s General Theory of Relativity actually predate the 1919 eclipse by a few years and continued for several decades after. But getting good results was always a struggle due to expenses, travel, eclipse circumstances, weather, war, equipment failure and conditions on the ground. Expeditions often hauled in tons of gear to the observation site — much in advance of the event itself. These experiments were carried out by a team of people funded by research grants.
The most recent attempt to repeat the experiment, that made Einstein a household name, came at the August 21, 2017 Great American Eclipse. Dr. Donald Bruns, a retired optical physicist and 50-year amateur astronomer, was inspired by the idea that readily available, modern, amateur equipment could best the accuracy of this experiment conducted by professionals over the last century.
What would Eddington have thought of Brun’s modest looking setup: a Tele Vue-NP101is (Nagler-Petzval APO) telescope with Finger Lakes Instrumentation Microline 8051 CCD camera mounted on a Software Bisque MyT Paramount with field tripod. All the gear fit in his automobile for transport to the Casper, WY observing site right before the event. Bruns carried out the imaging solo with just a laptop computer connected to his gear. Having automated the imaging process, he just watched the eclipse while his 21st-century electronics did the work.
The NP101is has a flat, color-free image plane, perfect for creating these very accurate star images
Dr. Bruns explains that he choose the Tele Vue scope because he needed “to pinpoint the centers of star images to within 0.02-pixel, those stars falling near the edges and corners of each frame must be as sharp as the ones in the center. The NP101is has a flat, color-free image plane, perfect for creating these very accurate star images, and I can adjust the focuser so that the camera remains perfectly square to the optical axis.”
About the Tele Vue-NP101is Photo / Visual APO Refractor
Al Nagler took Petzval’s portrait lens concept and patented a fast telescope version for the purpose of testing eyepieces (the 5”, f/4 Multi-Purpose Telescope). By 2001, the NP101 (Nagler-Petzval) scope was the ultimate culmination of 30-years of refinement toward optical perfection for the “multi-purpose” concept. However, we did not rest on our laurels: with the CCD imaging revolution challenging telescope optics beyond anything ever placed at the focal plane, we were determined to make the NP series optically, mechanically, and functionally as perfect as possible for imaging on chips with up to 50-mm diagonal, without penalty to its near ideal visual operation. The resulting NP101is is a 101-mm objective diameter, 540-mm focal length, f/5.4, APO (4-elements in 2-groups, Nagler-Petzval) refractor with a whopping 5.3° image circle at prime focus. Maximum visual field-of-view is likewise huge: 4.9° with 55-mm Plössl (10x) or 41-mm Panoptic (13x).
Calculations though, weren’t any faster than 100-years ago: after months of data reduction, Dr. Bruns arrived at the conclusion that starlight passing at the very edge of the sun would deflect by 1.7512-arcseconds. Based on Einstein’s equations, he calculated the theoretical value as 1.7512-arcseconds — exactly the same! He admits it was a coincidence that the numbers agreed as he calculated the experimental value with an uncertainty of 3%. The last professional attempt, at the 1973 eclipse, achieved an error of 11%. Dr. Bruns had succeeded in besting the pros using modern equipment on a modest-sized scope!
For his groundbreaking efforts conducting this experiment as an amateur astronomer, Dr. Bruns received the American Astronomical Society’s Chambliss Amateur Achievement Award. His award citation reads: “For his successful recreation of, and improvement upon, Eddington’s iconic deflection-of-light experiment during the 2017 total solar eclipse, which represents a tour de force in careful observing and calibration.”
Tele Vue Optics congratulates Dr. Bruns on this outstanding achievement and thanks him for selecting our Tele Vue-NP101is refractor to have been part of eclipse history.
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