Editing Alvan Graham Clark (section)

==Biography==
Alvan Graham Clark was born in [[Fall River, Massachusetts|Fall River]], [[Massachusetts]], the son of [[Alvan Clark]], founder of [[Alvan Clark & Sons]].<ref name=Cyclopaedia>{{Cite book |url=https://books.google.com/books?id=4FxDAQAAMAAJ&pg=PA386 |title=The National Cyclopaedia of American Biography |volume=V |publisher=James T. White & Company |page=386 |year=1907 |access-date=2021-04-02 |via=Google Books}}</ref>

On January 31, 1862, while testing a new {{convert|18.5|in|mm|adj=on}} aperture [[great refractor]] telescope in [[Cambridgeport]], [[Massachusetts]], Clark made the first ever observation of a [[white dwarf]] star.  This discovery of [[Sirius#Sirius B|Sirius B]], or affectionately "the Pup", proved an earlier hypotheses ([[Friedrich Wilhelm Bessel]] in 1844) that [[Sirius]], the brightest star in the night sky with an [[apparent magnitude]] of −1.46, had an unseen companion disturbing its motion.  Clark used the largest refracting telescope lens in existence at the time, and the largest telescope in the United States, to observe the magnitude 8 companion.

Clark's 18.5 inch refracting telescope was then delivered to his customer, the landmark [[Dearborn Observatory]] of [[Northwestern University]] in [[Evanston, Illinois]], where it is still being used today.<ref>[http://www.physics.northwestern.edu/about/dearborn-observatory/history.html Dearborn Observatory: History]</ref>

Alvan Graham Clark died in [[Cambridge, Massachusetts]] on June 9, 1897.<ref>{{Cite news |url=https://www.newspapers.com/clip/74960085/deaths/ |title=Deaths |newspaper=[[The Boston Globe]] |page=10 |date=1897-06-10 |access-date=2021-04-02 |via=Newspapers.com}}</ref>