Asteroids are somewhat arbitrarily differentiated from comets and meteoroids. Objects of interest include planets, moons, stars, nebulae, galaxies, and comets. Centaurs typically behave with characteristics of both asteroids and comets. Many comets and asteroids collided with Earth in its early stages. Research is involved in observations of near-Earth phenomena such as asteroids and comets. The dust is thought to be generated by collisions among comets and asteroids. This is a common size for asteroids, comets, and moons. This is behavior typical of comets but not asteroids. Bennu, Phaethon, and inactive Manx comets are examples of active asteroids. Astronomy includes the examination, study and modeling of stars, planets, comets, galaxies and the cosmos. Carbon is abundant in the Sun, stars, comets, and in the atmospheres of most planets. Long-period comets have orbits lasting thousands of years. This is useful for calculating the behaviour of planets and comets and such. Ejected Jupiter trojans could become temporary satellites of Jupiter or Jupiter-family comets. The first recorded observations of comets and supernovae were made in China.