Adriaan van Maanen, Dutch-American astronomer and academic (d. 1946)
Adriaan van Maanen (March 31, 1884 – January 26, 1946) was a Dutch–American astronomer.

Van Maanen, born into a well-to-do family in Friesland, studied astronomy at the University of Utrecht (earning his Ph.D. in 1911) and worked briefly at the University of Groningen. In 1911, he came to the United States to work as a volunteer in an unpaid capacity at Yerkes Observatory. Within a year he got a position at the Mount Wilson Observatory, where he remained active until his death in 1946.

He discovered Van Maanen's star.

He is well known for his astrometric measurements of internal motions in spiral nebulae. Believing that nebulae were local, stellar and gaseous systems that existed in our galaxy, his measurements came to be at odds with Edwin Hubble's discovery that the Andromeda Nebula and other spiral nebulae were extragalactic objects. The speed of rotation he calculated for the nebulae, if Hubble were correct as to their extragalactic nature, would have had their Cepheid stars moving at speeds faster than that of light. In 1935, it was decided that since Hubble's calculations of extragalactic Cepheid distances were correct, ergo van Maanen's astrometric measurements had to be incorrect.

In 1924 he became member of the Royal Netherlands Academy of Arts and Sciences.