Harlan James Smith (August 25, 1924–October 17, 1991) was an American astronomer.
He was born in Wheeling, West Virginia, the son of Paul and Anna McGregor Smith. While attending Wheeling High School he was named first runner up in the "Westinghouse National Science Talent Search". From 1943 until the end of World War II he served in the U.S. Army Air Corps, performing weather observation.
Following the war he attended Harvard University, earning a B.A. in 1949. In 1950 he married Joan Greene, and by 1951 had earned his M.S. degree from Harvard. He began teaching at the astronomy department at Yale University in 1953, but still completed his Ph.D. from Harvard by 1955.
In 1963 he was named chair of the University of Texas astronomy department where he also became the director of the McDonald Observatory. At the observatory he oversaw the construction of the 2.7m telescope he had persuaded NASA to build in support of planetary missions. From 1966 until 1970 he was a member of the Committee on the Large Space Telescope, an ad hoc group formed by the National Academy of Sciences, the work of which resulted in the Hubble Space Telescope. He also was the chairperson of the NASA Space Science Board from 1977 until 1980, and there helped propose NASA's Great Observatories program. He retired in 1989.During his career he studied variable stars, the radio emission from planets, as well as photometry and astronomical instruments. With Dorrit Hoffleit, he was the first to observe the optical variability of quasars, and discovered a class of variable stars known as Delta Scuti variables.
He was an enthusiastic proponent of educating the public on astronomy, and developed the radio program "Star Date". He also developed "The Story of the Universe", a series of educational films. He was also a proponent of international cooperation, particularly with China which he visited several times. He served as co-editor of the Astronomical Journal as well as acting secretary for the American Astronomical Society.
Smith died due to complications related to cancer. He was survived by his wife and four children, along with their grandchildren.