An
astronomical object or
celestial object is a naturally occurring
physical entity, association, or structure that current
science has demonstrated to exist in the
observable universe. The term
astronomical object is sometimes used interchangeably with
astronomical body. Typically, an astronomical (celestial) body refers to a single, cohesive structure that is bound together by
gravity (and sometimes by
electromagnetism). Examples include the
asteroids,
moons,
planets and the
stars. Astronomical objects are gravitationally bound structures that are associated with a position in space, but may consist of multiple independent astronomical bodies or objects. These objects range from single planets to
star clusters,
nebulae or entire galaxies. A
comet may be described as a body, in reference to the frozen nucleus of ice and dust, or as an object, when describing the nucleus with its diffuse coma and tail.