William Herschel, destined to become one of the world's great observational astronomers, was born in Germany but lived most of his life in England. By the age of 34 he had established himself as a musician of note: teaching music, playing the organ at Bath, giving violin concerts, and composing military music, symphonies, and choral works. His leisure hours, however, were devoted to studying foreign languages, philosophy, and mathematics. At age 35 his simmering interest in astronomy was fired into action when he read Smith's Compleat System of Opticks and Ferguson's Astronomy. Before long he was constructing his own reflecting telescopes.
By 1773, Herschel had built a telescope with a focal length of 5.5 ft, and he was now ready to begin observing. Between 1774 and 1781, he recorded observations of numerous individual objects. His study of the sky led him to several important discoveries. Herschel was searching for double stars with the expectation that a parallactic shift of the brighter component might be detected relative to the fainter and presumably more distant component. Instead, Herschel discovered that one star actually orbited around the other, the first tangible proof that gravity extended to stars. Out of this work came a first in its field the Catalogue of Double Stars.
Another program Herschel initiated was the examination of every star in the standard star charts of his day. On the night of March 13, 1781, he made the historic discovery of a new planet in the constellation of Gemini, the planet Uranus. This discovery won him international fame and the royal patronage of King George III. After being knighted and awarded an annual stipend by the king, Herschel could devote all his time to astronomy, unhindered by the necessity of earning a living as a professional musician.
One of Herschel's important discoveries was the Sun's motion in space. From the proper motions of only 13 stars he found that the Sun is moving in space relative to its stellar neighbors toward a point in the constellation Hercules not far from the bright star Vega.
His most ambitious undertaking was an attempt to determine the structure of the Milky Way system. This involved a technique Herschel called "star gauging": making sample counts of the stars in the field of view of his telescope. By the time he finished, nearly 20 years later in 1802, he had counted over 90,000 stars in 2400 sample areas. Along the way Herschel noted many objects of interest for future astronomers: variable stars, binary stars, dark areas in the Milky Way that looked like holes, irregular bright nebulosities, clusters of stars, and several thousand small nebulous objects or nebulae. The last three categories of objects were the subject of his 1802 Catalogue of Star Clusters and Nebulae. The Milky Way system, he concluded from his star counts, had the shape of a disk, like a grindstone, having a thickness of about one-sixth its diameter. The Milky Way was marked by many irregularities, and the Sun was located near its center. Later studies confirmed Herschel's deduction that our Galaxy is disk-shaped, but found that the Sun is not near the center and that the system is considerably larger than Herschel supposed.