Comet Holmes (official designation: 17P/Holmes) is a periodic comet in the Solar System, discovered by the British amateur astronomer Edwin Holmes on November 6, 1892. Although normally a very faint object, Holmes became notable during its October 2007 return when it temporarily brightened by a factor of about half a million, in what was the largest known outburst by a comet, and became visible to the naked eye. It also briefly became the largest object in the Solar System, as its coma (the thin dissipating dust ball around the comet) expanded to a diameter greater than that of the Sun (although its mass remained minuscule). It brightened to an approximate magnitude of 4 or 5 before fading from visibility over a period of several weeks. The first calculations of the elliptical orbit of 17P/Holmes were done independently by Heinrich Kreutz and George Mary Searle. Additional orbits eventually established the perihelion date as June 13 and the orbital period as 6.9 years. These calculations proved that the comet was not a return of Biela's Comet. The 1899 and 1906 appearances were observed, but the comet was lost after 1906 until it was recovered on July 16, 1964, by Elizabeth Roemer (US Naval Observatory Flagstaff Station, Arizona, United States). Aided by the computer predictions of Brian G. Marsden, the comet has been observed on every subsequent return.