Arthur Matthew Weld Downing (13 April 1850 – 8 December 1917) was a British astronomer.He was born in Carlow, Ireland.He became an assistant at the Royal Greenwich Observatory in 1873. He became superintendent of HM Nautical Almanac Office from 1891 to 1910. He was elected a Fellow of the Royal Society in June 1896 He collaborated with his U.S. counterpart Simon Newcomb in establishing an international standard for astronomical constants.