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Alcyoneus is an FR II class low-excitation radio galaxy which has the largest observed radio emission, with lobed structures spanning 5 megaparsecs (16×10 6 ly). For comparison, another similarly sized giant radio galaxy is 3C 236, with lobes 15 million light-years across.
In Western culture, the name "Milky Way" is derived from its appearance as a dim un-resolved "milky" glowing band arching across the night sky. The term is a translation of the Classical Latin via lactea, in turn derived from the Hellenistic Greek γαλαξίας, short for γαλαξίας κύκλος (galaxías kýklos), meaning "milky circle".
Galaxy morphological classification is a system used by astronomers to divide galaxies into groups based on their visual appearance. There are several schemes in use by which galaxies can be classified according to their morphologies, the most famous being the Hubble sequence , devised by Edwin Hubble and later expanded by Gérard de ...
This is in contrast to extragalactic astronomy, which is the study of everything outside our galaxy, including all other galaxies. Galactic astronomy should not be confused with galaxy formation and evolution , which is the general study of galaxies , their formation, structure, components, dynamics, interactions, and the range of forms they take.
Galaxies and galaxy clusters < 50 M ly away from Earth plotted in the supergalactic plane. The supergalactic coordinate system is a reference frame for the supercluster of galaxies that contains the Milky Way galaxy, referenced to a local relatively flat collection of galaxy clusters used to define the supergalactic plane.
The transition between Earth's atmosphere and outer space lacks a well-defined physical boundary, with the air pressure steadily decreasing with altitude until it mixes with the solar wind. Various definitions for a practical boundary have been proposed, ranging from 30 km (19 mi) out to 1,600,000 km (990,000 mi). [16]
The Andromeda Galaxy is a barred spiral galaxy and is the nearest major galaxy to the Milky Way. It was originally named the Andromeda Nebula and is cataloged as Messier 31, M31, and NGC 224. Andromeda has a D 25 isophotal diameter of about 46.56 kiloparsecs (152,000 light-years) [8] and is approximately 765 kpc (2.5 million light-years) from ...
A spiral galaxy is a type of galaxy characterized by a central bulge of old Population II stars surrounded by a rotating disc of younger Population I stars. A spiral galaxy maintains its spiral arms due to density wave theory.