William Weber Coblentz (November 20, 1873 – September 15, 1962) was an American physicist notable for his contributions to infrared radiometry and spectroscopy.

His mother (Catherine) died when Coblentz was just under three, leaving him temporarily with a family of just his younger brother (Oscar) and their father (David).

The family's extremely modest circumstances led to a somewhat-delayed education for Coblentz, who did not finish high school (Youngstown, Ohio) until 1896, when he was 22 years old.

He went on to earn MS (1901) and PhD (1903) degrees from Cornell University in Ithaca, New York, staying two years beyond his doctoral time by working as a Research Fellow with support from the Carnegie Institution.

[3] On acquiring his doctorate, he soon began publishing regularly on problems related to infrared (IR) radiation, both those concerning spectroscopy and those concerning radiometry.

In 1913, he developed thermopile detectors and used them at Lick Observatory to measure IR radiation from 110 stars, and the planets Mars, Venus, and Jupiter.

Extending this work, Coblentz and Carl Lampland, of the Lowell Observatory, measured large differences between the day and night temperatures on Mars, which implied a thin Martian atmosphere.

An inspection of Coblentz's bibliography shows that from about 1930 his research turned more toward measurements involving the ultraviolet (UV) region and away from infrared work.

He wed Catherine Emma Cate of Vermont on June 10, 1924, and it is said that they spent their honeymoon in Flagstaff, Arizona while Coblentz was at the Lowell Observatory measuring planetary temperatures.

Catherine Cate Coblentz achieved success as a writer of children's book, worked for a time at the National Bureau of Standards, and was instrumental in raising money to build the Cleveland Park Neighborhood Library in Washington, DC.