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18/08/1877 Asaph Hall discoveres Phobos

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The Moons of Mars Explained -- Phobos & Deimos MM#2

Hall was given responsibility for the USNO 26-inch telescope, the largest refracting telescope in the world at the time. It was with this telescope that he discovered Phobos and Deimos in 1877. Hall also noticed a white spot on Saturn which he used as a marker to ascertain the planet's rotational period.