An astronomical object or the celestial object refers to a naturally taking place physical entity, composition, or association, which prevails in the observable universe. Or it can also be illustrated as the celestial body refers to any natural body external to the atmosphere of the Earth. The examples, are the Sun, Moon, and the planets of the solar system.
In the mentioned objects, the lowest in the hierarchy is the planet, then comes the star, then the solar system, and finally the galaxy.