William Herschel, born this day in 1738, was a promising young composer, a German contemporary of Haydn who composed 24 symphonies before his 26th birthday. He played oboe, violin and harpsichord, moved to England and later became chief organist at the cathedral of Bath, and later director of their symphony orchestra.
Herschel’s second career was in astronomy. He constructed one of the largest telescopes of his day, with a 50 inch mirror and 40-foot tube, and he made a systematic search of the sky for double stars. His catalog helped to resolve the fundamental question: how far away are the stars? Double stars are in orbit about each other, and they can be seen to move over months and years. From the timing, Newton’s laws of motion determine the absolute scale of the orbital size, and thus the distance of the star system could be deduced.