March 8: Alvan Clark

Alvan Clark

March 8, 1804 – August 19, 1887

Alvan Clark, born in Ashfield, Massachusetts, the descendant of a Cape Cod whaling family of English ancestry, was an American astronomer and telescope maker. 

He was a portrait painter and engraver, but at the age of 40 become involved in telescope making. Using glass blanks made by Chance Brothers of Birmingham and Feil-Mantois of Paris, his firm Alvan Clark & Sons ground lenses for refracting telescopes, including the largest in the world at the time: 

• the 18.5-inch (470 mm) at Dearborn Observatory at the Old University of Chicago (the lens was originally intended for Ole Miss) 
  
• the 26-inch (660 mm) at the United States Naval Observatory, 
• the 30-inch (760 mm) at Pulkovo Observatory (destroyed in the Siege of Leningrad; only the lens survives) 
  
• the 36-inch (910 mm) telescope at Lick Observatory (still third-largest) 
  
• the 40-inch (1,000 mm) at Yerkes Observatory, which remains the largest successful refracting telescope in the world
  

He was the first person in the United States to make achromatic lenses, and the most important modern telescopes have been constructed at his factory in Cambridge-port. Mr. Clark invented numerous improvements in telescopes and their manufacture, including the double eye-piece, an ingenious method of measuring small celestial arcs. A list of discoveries made by him with telescopes of his own manufacture is given in the "Proceedings of the Royal Astronomical Society" (London, vol. 17, No. 9).

Mr. Clark accompanied the total-eclipse expedition to Jerez, Spain, in 1870, and also the similar expedition to Wyoming in 1878. As an independent observer he has discovered fourteen intricate double stars, including the companion to Sirius, for which the Lalande gold medal was awarded him by the French academy of sciences in 1862. He has also made numerous inventions connected with the manufacture of refracting telescopes. 

One of Clark's sons, Alvan Graham Clark, discovered the dim companion of Sirius. His other son was George Bassett Clark; both sons were partners in the firm.

The Lunar crater Clark and on Mars are named in his honor.