Template:Are You Sure/September 25
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A diagram of Jupiter (B) eclipsing its moon Io (DC) as viewed from different points in earth's orbit around the sun. From Olaf (Ole) Roemer, "Demonstration tovchant le mouvement de la lumiere trouvé par M. Römer de l' Academie Royale des Sciences," December 7, 1676.
• ... that astronomer and instrument maker Ole Rømer made the first quantitative measurements of the speed of light?