Heavenly bodies in astronomy are natural bodies visible in the sky. These are also known as celestial bodies. These bodies do not include man-made objects, such as satellites. Examples of heavenly or celestial bodies include planets, stars, dwarf planets and quasars.
The term astronomical object is also used to define naturally occurring physical entities that are observable in the universe. These objects are typically single cohesive structures such as asteroids, moons, planets and stars. Astronomical, heavenly or celestial bodies differ from astronomical objects. Astronomical objects are associated with a position in space, but these objects may not be a single cohesive structure, such as a star. They are often a grouping of many objects, such as a star cluster, nebula or galaxy. A comet can be defined as both an object and a body. It can be described as a body when referring to its nucleus alone or as an object when referring to its nucleus and tail.
The observable universe can be seen as having a hierarchical structure. The fundamental component of assembly at large scales is the galaxy. Galaxies are grouped into clusters and superclusters. These structures are spread out over thousands, millions or even billions of light years.