Extragalactic astronomy is the branch of astronomy

Astronomy

Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...

 concerned with objects outside our own Milky Way

Milky Way

The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

 Galaxy. In other words, it is the study of all astronomical objects which are not covered by galactic astronomy

Galactic astronomy

Galactic astronomy is the study of our own Milky Way galaxy and all its contents. This is in contrast to extragalactic astronomy, which is the study of everything outside our galaxy, including all other galaxies....

, the next level of galactic astronomy.

As instrumentation has improved, more distant objects can now be examined in detail. It is therefore useful to sub-divide this branch into Near-Extragalactic Astronomy and Far-Extragalactic Astronomy. The former deals with objects such as the galaxies

Galaxy

A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...

 of our Local Group

Local Group

The Local Group is the group of galaxies that includes Earth's galaxy, the Milky Way. The group comprises more than 30 galaxies , with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy...

, which are close enough to allow very detailed analyses of their contents (e.g. supernova remnant

Supernova remnant

A supernova remnant is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar material it sweeps up and shocks along the way.There are two...

s, stellar associations). The latter describes the study of objects sufficiently far away that only the brightest phenomena are observable.

Some topics include:

• Groups and clusters of galaxies
• Quasar
  Quasar
  A quasi-stellar radio source is a very energetic and distant active galactic nucleus. Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than...
  
  s
• Radio galaxies
  Radio galaxy
  Radio galaxies and their relatives, radio-loud quasars and blazars, are types of active galaxy that are very luminous at radio wavelengths, with luminosities up to 1039 W between 10 MHz and 100 GHz. The radio emission is due to the synchrotron process...
  
  
• Supernova
  Supernova
  A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
  
  e
• Intergalactic stars
• Intergalactic dust
  Intergalactic dust
  Intergalactic dust is cosmic dust in between galaxies in intergalactic space. Evidence for intergalactic dust has been suggested as early as 1949, and study of it grew throughout the late 20th century. There are large variations in the distribution of intergalactic dust...
  
  
• Intergalactic dust clouds

See also

• Galaxy color-magnitude diagram
  Galaxy color-magnitude diagram
  The Galaxy color-magnitude diagram shows the relationship between absolute magnitude, luminosity, and mass of galaxies. A preliminary description of the three areas of this diagram was made in 2003 by Eric F. Bell et al...
  
  
• Galaxy formation and evolution
  Galaxy formation and evolution
  The study of galaxy formation and evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies change over time, and the processes that have generated the variety of structures observed in nearby...
  
  
• Observational cosmology
  Observational cosmology
  Observational cosmology is the study of the structure, the evolution and the origin of the universe through observation, using instruments such as telescopes and cosmic ray detectors.-Early observations:...