A comet is an icy small Solar System body (SSSB) that, when close enough to the Sun, displays a visible coma (a thin, fuzzy, temporary atmosphere) and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet. Comet nuclei range from a few hundred meters to tens of kilometers across and are composed of loose collections of ice, dust and small rocky particles. Comets have been observed since ancient times.
Comets have a wide range of orbital periods, ranging from a few years to hundreds of thousands of years. Short-period comets originate in the Kuiper belt, or its associated scattered disc, which lie beyond the orbit of Neptune. Longer-period comets are thought to originate in the Oort cloud, a hypothesized spherical cloud of icy bodies in the outer Solar System. Long-period comets plunge towards the Sun from the Oort cloud because of gravitational perturbations caused by either the massive outer planets of the Solar System (Jupiter, Saturn, Uranus, and Neptune), or passing stars. Rare hyperbolic comets pass once through the inner Solar System before being thrown out into interstellar space along hyperbolic trajectories. Exocomets, comets beyond our solar system, have also been detected and may be common in the Milky Way Galaxy.
Comet McNaught, also known as the Great Comet of 2007 and given the designation C/2006 P1, is a non-periodic comet discovered on August 7, 2006 by British-Australian astronomer Robert H. McNaught using the Uppsala Southern Schmidt Telescope. It was the brightest comet in over 40 years, and was easily visible to the naked eye for observers in the Southern Hemisphere in January and February 2007.
With an estimated peak magnitude of −5.5, the comet was the second brightest since 1935. Around perihelion on January 12, it was visible worldwide in broad daylight. Its tail measured an estimated 35 degrees in length at its peak.
The brightness of C/2006 P1 near perihelion was enhanced by forward scattering.