Sidney Dean Townley (April 10, 1867 – March 18, 1946) was an American astronomer and geodeticist.
Born in Waukesha, Wisconsin.
He graduated the University of Wisconsin-Madison with distinction and became a member of Phi Beta Kappa.
Among many other posts Townley served as an instructor of astronomy at the University of Michigan and the University of California he was also the president of the Astronomical Society of the Pacific in 1916.
Throughout the course of his career he published around 100 academic papers and edited many more, he was recognised for his excellent editorial skills.