Kirkwood, Daniel (1814–1895)
American astronomer best known for his discovery (1866) of radial gaps in
the main asteroid belt, now known as
Kirkwood gaps. Kirkwood was also the first
to account for the Cassini and Encke Divisions in Saturn's
rings in terms of orbital resonances
with the planet's larger moons, and to propose the existence of a group
of sun-grazing comets.