November 5 – Joseph-Nicholas Delisle

Joseph-Nicholas Delisle may be best known for being an astronomer, but his journey to the historic observation of the transit of Mercury began out of obscurity.  He was one of twelve children born to history and geography teacher.  Evidently, his father’s love of learning, especially in the areas of science, projected young Delisle on the path towards a career in science.  He began his career teaching mathematics and astronomy at the College de France.  However, his love of astronomy soon began to set the course of his life.  After witnessing a solar eclipse on May 12, 1706, he was so fascinated by the phenomena that he took up residence in the dome of the Luxenbourg palace.  In May of 1724, he finally was able to witness a full eclipse from his ideal quarters.  His diffraction theory, though, is what set him  on the path towards notoriety and acclaim.  This theory led him to be recognized at the English Royal Society.  While it was not until almost a century later that the theory was officially confirmed by Dominique-Francois-Jean Arago through experimentation, Delisle was one of the first to observe the phenomena on the sun.  What Delisle found was that a bright spot would be seen in the center of a circular object’s shadow.  This bright spot was formed by diffraction.  This observation by Delisle became important to the understanding of the nature of light.  Once in England, Delisle had the opportunity to meet quite a few famous people, including Isaac Newton.  However, Delisle’s real success was still to come.  In 1725, he was invited by the ruling family of Russia to come to St. Petersburg.  While in Russia, he became very well-known.  He was a member of the Imperial Academy of Science and the director of the St. Petersburg Observatory.  Although he only intended to spend 4 years in Russia, he ended up spending about 22 years there and trained the first generation of Russian astronomers.  Beyond training others, Delisle also went on expeditions to get more observations.  On November 5, 1743, he authored a letter to his friend Cassini, which outlined a method for observing the transit of Mercury.  His methods were later put into practice and are credited with finding the transit of Mercury and Venus.  Finally in 1747, Delisle moved back to Paris, where he continued to teach.  He died on September 12, 1768 from apoplexy.  While he is often forgotten among the great scientists, he did set the stage for many important discoveries in the field of astronomy.



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