A meteor procession occurs when an Earth-grazing meteor breaks apart, and the fragments travel across the sky in the same path. According to physicist Donald Olson, only four occurrences are known:18 August 1783 Great Meteor. 20 July 1860 Great Meteor; sighted over North America, believed by Olson to be the event referred to in Walt Whitman's poem Year of Meteors, 1859–60 21 December 1876 Great Meteor; sighted over Kansas, Missouri, Illinois, Indiana, Ohio, Pennsylvania 9 February 1913 Great Meteor Procession; a chain of slow, large meteors moving from northwest to southeast, sighted over North America, particularly in Canada, the North Atlantic and the Tropical South Atlantic