Alvan Clark & Sons was an American company founded in the 19th century, known for manufacturing high-quality telescopes. Established in 1852 by Alvan Clark, the company gained a reputation for producing large refracting telescopes, which were used by observatories around the world. Their craftsmanship and attention to detail made them a leader in the field of optical instruments. The company was particularly famous for its work on the Great Refractor at the Yerkes Observatory, which was completed in 1897. Alvan Clark & Sons contributed significantly to the advancement of astronomy by providing telescopes that enhanced the study of celestial bodies.