Asaph Hall Jr.

Asaph Hall IV (October 6, 1859 – January 12, 1930), known as Asaph Hall Jr., was an American astronomer. He was the son of Asaph Hall, who discovered the moons of the planet Mars. One of his brothers was Percival Hall.

Early life Hall was born in Cambridge, Massachusetts in 1859. He was the son of the astronomer Asaph Hall and the mathematician Angeline Stickney Hall. His father was best known for having discovered the two moons of Mars, Deimos and Phobos. He grew up in Washington, D.C., where his father worked at the United States Naval Observatory. He attended the Columbian College in the District of Columbia (now George Washington University) and then Harvard University, where he received his undergraduate degree in 1882.

After graduation Hall became an assistant astronomer at the Naval Observatory from 1882-1885. Hall used the Yale heliometer to determine the mass of Saturn using the orbit of Titan when writing this thesis paper. His results confirmed Bessel's measurement. After receiving his PhD, Hall returned to the Naval Observatory until 1892, when he then took over the responsibilities as Director of the Detroit Observatory and professor of astronomy at the University of Michigan.

Subsequent career Hall's childhood home, in the Georgetown neighborhood of Washington, D.C. Note his mother Angeline on front steps, and two Black workers. The house later served as the parsonage and fellowship hall of Alexander Memorial Baptist Church. During his time at the University of Michigan, he repaired the meridian circle and used it to do a determination of the constant of aberration. Hall made this determination with the newly repaired Meridian Circle, by examining zenith distances from Polaris. using the 26-inch (66-cm) telescope, the great refractor of his father's discoveries. He retired in 1929 and died the following year. He is buried in Arlington National Cemetery.

Personal life In 1897, Asaph Hall Jr. married Mary Estella Cockrell who he later had two children with, Katherine and Mary. Outside of his actual astronomical work, Hall also was influential in securing fair pay for the other workers around him at the U.S. Naval Observatory. In addition, Hall was very dedicated to expanding and improving the library of the Naval Observatory when he was not conducting his research. After retiring in 1929, Hall moved to Upper Darby, Pennsylvania, near the Flower Observatory operated by the University of Pennsylvania. There, he spent the remainder of his life working as a volunteer observer until his death on January 12, 1930.