Forest Ray Moulton

Today is the birthday of astronomer Forest Ray Moulton, born in LeRoy, Michigan, in 1872. He grew up in a log cabin and became the first boy in his town to get a university education when he attended Albion College. Moulton received a Ph.D. in math and astronomy from the University of Chicago in 1899. Moulton is best known for the planetesimal hypothesis, which he developed with geologist T. C. Chamberlin to explain why the planets revolve around the sun in nearly circular orbits along roughly the same plane. The scientists proposed that a swarm of small rocks (planetesimals) swirling around the sun coalesced into the planets. Although parts of their idea are no longer accepted—they proposed that a close rendezvous with another star led to the swarm—the concept of planetesimals coalescing into planets has stood the test of time. Here is a quote from one of Moulton’s books: “To an astronomer the most remarkable and interesting thing about that part of the physical universe with which he has become acquainted is not its vast extent in space, nor the number and great masses of its stars, nor the violent forces that operate in the stars, nor the long periods of astronomical time, but that which holds him awestruck is the perfect orderliness of the universe and the majestic succession of the celestial phenomena.”

Date in History: 29 April 1872