A comet is an icy object which is present in Solar System object that, when travelling close to the Sun, it warms and start to emit gases, a practice known as outgassing. This creates a visible atmosphere or coma, and sometimes also a tail. These occurrences are due to the effects of solar radiation and the solar wind acting upon the core of the comet. Comet core range from a few hundred meters to tens of kilometres across and are made up of loose collections of ice, dust, and small rocky particles. The coma can be up to 15 times the Earth's diameter, while the tail may give one astronomical unit. If satisfactorily bright, a comet may be seen from the Earth without the help of a telescope and may subtend an arc of 30° (60 Moons) through the sky. Comets have been seen and recorded since ancient times by many cultures.Comets are distinguished from asteroid-ds by the existence of an extended, gravitationally unbound atmosphere nearby their central core. This atmosphere has parts named as the coma which is surrounded by its nuclei (the central part immediately surrounding the core) and the tail (a usually linear section consisting of dust or gas is blown emitting out from the coma by the Sun's RAYS pressure or out streaming solar air plasma). However, dead comets that have passed close to the Sun several times and have lost nearly all of their volatile ices and dust and may come to resemble minor asteroids. Asteroids are assumed to have a different origin than comets, having formed around Jupiter orbit rather than in the outer Solar System. The discovery of main-belt comets and lively centaur minor planets has a fuzzy distinction between asteroids and comets. In the first period of the 21st century, there was the discovery of some minor bodies with long-period comet orbits, but features of inner solar system asteroids were called Manx comets.