Alvan Clark. Portrait of Alvan Clark (1804-87), American astronomer and telescope maker. A direct descendent of a Mayflower immigrant, Clark was a talented painter and portrait painter. When he was 40 his elder son became interested in telescopes. Clark shared his son's interest and they began making telescopes, establishing America's first telescope firm. Many of their instruments are still in use. In 1897 the firm built the world's largest refracting telescope; the Yerkes telescope has a 101 centimetre (40 inch) lens. Clark also discovered two new binary stars, one being 8 Sextantis. His younger son, Alvan Graham Clark, discovered the star Sirius B in 1862.