Oort Cloud objects, artwork. Objects within the Oort Cloud, a postulated cloud of comet nuclei surrounding the Solar System. The rest of the Oort Cloud is seen edge-on in the background, forming a spherical shell around the Sun (upper centre). The horizontal band is the material in the plane of the planetary orbits (the ecliptic), forming the Kuiper Belt in the region nearer to the Sun. The Oort Cloud is thought to extend over a light year from the Sun, up to a distance of about 100,000 astronomical units (AU). One AU is the distance from the Earth to the Sun, some 150 million kilometres. The existence of the Oort Cloud is inferred from the orbits of long-period comets that take millions of years to orbit the Sun.