An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

Of, pertaining to, or dealing with the space beyond the Milky Way.

From → extra- + → galactic.

The branch of astronomy that deals with objects beyond the Milky Way, especially galaxies and quasars.

→ extragalactic; → astronomy.

The integrated intensity of all of the light emitted throughout the history of the Universe across the whole of the → electromagnetic spectrum, including those which are not individually detected. The EBL spectrum includes cosmological backgrounds associated with either primordial phenomena, such as the → cosmic microwave background radiation (CMBR), or photons emitted by stars, galaxies and → active galactic nuclei (AGN) due to → nucleosynthesis or other → radiative processes, including → dust scattering, → absorption and reradiation. The EBL may also contain signals that are diffuse and extended, including high-energy photons associated with dark matter particle decays or annihilation.

→ extragalactic; → background; → light.