Alvan Clark and his assistant Carl Lundin (right) alongside the 40-inch lens
Nothing is known of Clark's education.
Clark was the son of Alvin Clark, the founder of Alvan Clark & Sons. He joined his father and brother in the business in the early 1850's. Recognition of the family’s superb lenses was slow to come. The discovery of two double stars by the elder Alvan Clark in the late 1850's, however, attracted attention abroad, and the firm began to flourish.
They made the 36-inch (91-centimetre) lens for the Lick Observatory, Mount Hamilton, California (1888); the 30-inch lens for the Pulkovo Observatory, near St. Petersburg in Russia (1878); the 28-inch for the University of Virginia, Charlottesville (1883); and 24-inch lenses for the U.S. Naval Observatory, Washington, D.C. (1873), and the Lowell Observatory, Flagstaff, Arizona (1896). All these telescopes remain in operation except that at Pulkovo, which was destroyed during World War II.
Clark directed the fabrication of the 40-inch lens of the Yerkes Observatory, Williams Bay, Wisconsin, the largest refractor lens in the world. Using telescopes of his own construction, he discovered the companion of the star Sirius as well as 16 double stars.
Clark married Mary Mitchell Willard Clark on January 2, 1865. Together, they had 4 children.