Locality in
astronomy
Astronomy () is a natural science that studies astronomical object, celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and chronology of the Universe, evolution. Objects of interest ...
is in theory closeness of the observer relative to the observed astronomical phenomenon under consideration, and thus in practice the relative closeness of the phenomenon to the
star system
A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a '' star cluster'' or ''galaxy'', although, broadly speakin ...
of the
Sun.
Being local is an ambiguous condition, and always relative to the
order of magnitude of the relevant phenomenon. The term "local" is commonly applied to structures on five successively larger scales beyond the roughly two-light-years diameter of the
Solar System
The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...
:
* The
Local Interstellar Cloud containing the Solar System, roughly 30 light years across
* The
Local Bubble of gas in turn containing it, 300 light years or more across
* The Local Arm, a.k.a. the
Orion Arm (of the
Milky Way
The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked ey ...
galaxy
A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar Sys ...
), 3,500 light years wide, and approximately 10,000 long
* The
Local Group, the group of galaxies that contains the Milky Way, 10 million light-years across
* The Local Supercluster or
Virgo Supercluster, 110 million light-years across
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