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 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). Discovery Comet Holmes was discovered by Edwin Holmes on November 6, 1892, while he was conducting regular observations of the Andromeda Galaxy (M31). Its discovery in 1892 was possible because of an increase in its magnitude similar to the 2007 outburst; it brightened to an approximate magnitude of 4 or 5 before fading from visibility over a period of several weeks. The comet's discovery was confirmed by Edward Walter Maunder (Royal Observatory, Greenwich, England), William Henry Maw (Kensington, London, England), and B. Kidd (Bramley, Surrey, England). Independent discoveries were made by Thomas David Anderson (Edinburgh, Scotland) on November 8 and by Mike Brown (Wilkes, USA) and by John Ewen Davidson (Mackay, Queensland, Australia) on November 9. 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 (see Lost comet) 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. 2007 outburst During its 2007 return, Holmes unexpectedly brightened from a magnitude of about 17 to about 2.8 in a period of only 42 hours, making it visible to the naked eye. This represents a change of brightness by a factor of a million and is the largest known outburst by a comet thus far. The outburst took place from October 23 to 24, 2007. The first person reportedly to notice a change was J. A. Henríquez Santana