American astronomer known for being a believer of the Chamberlin-Moulton planetesimal hypothesis, which says planets formed from smaller parts.
He finished his graduate studies at the University of Chicago, receiving a Ph.D. in 1899.
The moon crater 'Moulton' is named in his honor.
He was born and raised in Le Roy, Michigan.
He and Edwin Hubble were both famous American astronomers.
