August 12th, 1877 – Martian Moon Discovered!


In the 1870’s the lead authority on Mars was not H.G. Wells; it was American astronomer Asaph Hall who discovered the Martian moon Deimos on August 12th, 1877.

Asaph Hall

In 1856, Hall took a job at the Harvard College Observatory in Cambridge, Massachusetts, and turned out to be an expert computer of orbits. Hall became assistant astronomer at the US Naval Observatory in Washington DC in 1862, and within a year of his arrival he was made professor.


Asaph Hall III (October 15th, 1829 – November 22nd, 1907)

In 1875 Hall was given responsibility for the USNO 26-inch (66-cm) telescope, the largest refracting telescope in the world at the time. It was with this telescope that he discovered Phobos and Deimos in August 1877. Hall also noticed a white spot on Saturn which he used as a marker to ascertain the planet’s rotational period. In 1884, Hall showed that the position of the elliptical orbit of Saturn’s moon, Hyperion, was retrograding by about 20° per year. Hall also investigated stellar parallaxes and the positions of the stars in the Pleiades star cluster.

Hall won the Lalande Prize of the French Academy of Sciences in 1878, the Gold Medal of the Royal Astronomical Society in 1879, the Arago Medal in 1893, and was made a Chevalier in the Ordre national de la Légion d’honneur (French Legion of Honor) in 1896. Hall crater on the Moon as well as Hall crater on the Martian moon Phobos are named in his honor. Asteroid 3299 Hall is also named in his honor.


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