Two moons of Mars, Phobos and Deimos, were identified by Asaph Hall in 1877 using the 26-inch refractor at the Old Naval Observatory. This achievement established his standing in nineteenth-century science, securing his legacy as an astronomer who transitioned from a background in manual labor to a career defining the celestial mechanics of the solar system.
Early Life and Education
Born in 1829 in Goshen, Connecticut, Hall faced financial hardship following his father's death when he was thirteen. He left formal schooling at sixteen to apprentice as a carpenter. He eventually attended New-York Central College in McGrawville, where he studied mathematics and geometry under Angeline Stickney. They married in 1856, the same year he began his professional trajectory at the Harvard College Observatory.
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Hall joined the US Naval Observatory in 1862 and attained the rank of professor within a year. His work involved calculating orbits and stellar parallaxes. In 1872, he documented an early instance of random sampling in scientific inquiry through an experiment using a steel wire to approximate pi, a precursor to the modern Monte Carlo method. Beyond his orbital calculations, he determined the mass of Mars and identified a white spot on Saturn to calculate the planet's rotation.
The Search for Martian Moons
During the 1877 opposition of Mars, Hall intensified his search for satellites, a task encouraged by his wife, Angeline Stickney. After initial sightings were hindered by atmospheric conditions, he confirmed the existence of Deimos on August 12 and Phobos on August 18. He formally announced these findings after verifying the objects moved in tandem with the planet, a process he shared with his assistant George Anderson and colleague Professor Newcomb.
Later Years and Legacy
Retiring from the Navy in 1891, Hall served as a lecturer in celestial mechanics at Harvard University between 1896 and 1901. His professional honors included the 1877 Lalande Prize, the 1879 Gold Medal of the Royal Astronomical Society, and his 1896 appointment as a Knight of the Legion of Honour. He died in 1907 while visiting his son in Annapolis and was buried at the East Street Cemetery.
Fast facts
- Born: 1829, Goshen, Connecticut
- Died: 1907, Annapolis, Maryland
- Major discovery: Phobos and Deimos (1877)
- Professional occupations: Astronomer, mathematician, carpenter
- Education: New-York Central College
- Wife: Angeline Stickney
- Awards: Knight of the Legion of Honour (1896), Lalande Prize (1877)
Questions readers ask
What method did Asaph Hall use to calculate pi?
He employed an early form of random sampling involving throwing a steel wire onto a surface marked with parallel lines, later known as the Monte Carlo method.
Where did Asaph Hall discover the moons of Mars?
He discovered them at the Old Naval Observatory in Washington, D.C., using the 26-inch refracting telescope.
Achievements
- Knight of the Legion of Honour — 1896
- Affiliated with Harvard University and Old Naval Observatory
- Worked as astronomer, mathematician and carpenter
