The development of the photoelectric method for investigating weakly variable stars and spectroscopic investigations with the 122 cm telescope made the Babelsberg observatory well-known beyond Europe, too.
2.
For his research he used a glossmeter with a specular angle of 45?as did most of the first photoelectric methods of that type, later studies however by Hunter and Judd in 1939, on a larger number of painted samples, concluded that the 60 degree geometry was the best angle to use so as to provide the closest correlation to a visual observation.
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