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§ 1. The blue sunlit auroral rays on March 23, 1920 —Since my permanent auroral stations in southern Norway were established in 1911, sunlit auroral rays have been observed and measured about 50 times, but among these, blue ones have occurred only on two occasions, the first March 23, 1920, and the second September 15, 1938, both before sunrise. A report on the blue rays of March 23, 1920, is given in a paper covering the period 1911‐1922. l From this paper we quote the following description:
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Carl Störmer (1939) studied this question.
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