Bart Jan Bok (Hoorn, April 28, 1906 – Tucson, August 5, 1983) was a Dutch-American astronomer.

He was born in the Netherlands, and educated at the Leiden and Groningen Universities. In 1929 he married fellow astronomer Dr. Priscilla Fairfield Bok, and for the remainder of their lives the two collaborated closely on their astronomical work.

From 1929 until 1957 he worked at Harvard University. He then worked as director of Mount Stromlo Observatory in Australia for nine years, before returning to the United States as director of Steward Observatory. He became a US citizen in 1938.

In 1975 Bok coauthored the statement Objections to Astrology (The Humanist, 1975)[1], which was endorsed by 186 professional astronomers, astrophysicists, and other scientists, including nineteen winners of the Nobel Prize. The statement was published in The Humanist. This led to the formation of the Committee for the Scientific Investigation of Claims of the Paranormal, of which he was a founding Fellow.

Bart Bok was an exceedingly popular personality in the field of astronomy, noted for his affability and humor. The Asteroid 1983 Bok was named for him while he was still living. In the ceremony announcing the award, he thanked the IAU for giving him "a little plot of land that [I] can retire to and live on." He participated in or led several groups to view solar eclipses, the last near Irkutsk in Siberia in the summer of 1980. On this trip to the USSR he led the group on a side trip to Byurakan Observatory, meeting with the director, Victor Ambartsumian.

Bok died of a heart attack at his home in Tucson, Arizona.