1890-1960

British astronomer best known for his precise determination of the astronomical unit (distance between Earth and Sun), which thus established the scale of the solar system. Jones photographed the asteroid Eros over 1,200 times during its 1930-31 close approach, and after 10 years of data analysis announced the astronomical unit to be 93 million miles (149,668,992 km). Jones also showed that Earth's rate of rotation was not constant. He served as the tenth astronomer royal (1933-55).