Astronomical object
An astronomical object is a naturally occurring physical entity or structure in space, including planets, stars, nebulae, and galaxies.
Planet: A nearly round body orbiting a star or stellar remnant that has cleared its orbital neighborhood. Planets are among the most familiar compact objects in space.
Astronomy: The scientific study of celestial objects, phenomena, and the universe. Astronomy investigates the objects and structures described on this page.
Electromagnetic spectrum: The full range of electromagnetic radiation, ordered by wavelength or frequency. Different wavelengths reveal different properties of astronomical objects.
Astronomical transient: A short-lived astronomical event or source whose brightness changes significantly over time. A transient is an event or changing source, not necessarily a durable object.
Dark matter: Matter inferred from gravitational effects that does not emit, absorb, or reflect detectable light. Its physical nature is unknown despite its gravitational influence on galaxies and clusters.
Star: A self-gravitating sphere of hot plasma that produces energy through nuclear fusion or its aftermath. Stars are luminous, massive objects that shape their surroundings.
Interstellar medium: The gas and dust that occupy the space between stars in a galaxy. It supplies material to some objects and is altered by others.
Spectroscopy: The study of how matter emits, absorbs, or scatters electromagnetic radiation as a function of wavelength. Spectra reveal an object's composition, temperature, and motion.
Space debris: Human-made objects and fragments left in orbit around Earth or other bodies. Space debris is artificial, unlike the naturally occurring entities defined here.
Dark energy: A name for the cause of the universe's accelerated expansion, often modeled as a uniform energy component. It affects cosmic structure but is not established as an astronomical object.