English astronomer who failed to take the advice of John Couch Adams on where to search for the planet Neptune, leaving its discovery to French and German astronomers.
Challis was born in Braintree, Essex, and educated at Cambridge. An Anglican cleric, he was rector at Papworth Everard, Cambridgeshire, 1830-52, as well as professor of astronomy and director of the observatory at Cambridge from 1836.
In 1844, astronomer and mathematician Adams obtained via Challis data from the Greenwich Observatory regarding the known deviations in the orbit of the planet Uranus. These indicated the gravitational influence of a planet even farther out. In Sept 1845 Adams supplied Challis and Astronomer Royal George Airy with an estimated orbital path for the unknown planet and a prediction for its likely position on 1 Oct 1845. But Challis did not take the calculations seriously and Airy did not even see them until the following year.
By that time, the new planet had been discovered from the Berlin Observatory. Challis admitted that if he had indeed conducted a search at Adams's predicted position for 1 Oct 1845 he would have been within 2° of the planet's actual position and would almost certainly have spotted it.