A galactic quadrant, or quadrant of the Galaxy, is one of four

circular sector A circular sector, also known as circle sector or disk sector or simply a sector (symbol: ⌔), is the portion of a disk (a closed region bounded by a circle) enclosed by two radii and an arc, with the smaller area being known as the ''minor ...

s in the division of the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

Galaxy.

Quadrants in the galactic coordinate system

In actual astronomical practice, the delineation of the galactic quadrants is based upon the

galactic coordinate system The galactic coordinate system is a celestial coordinate system in spherical coordinates, with the Sun as its center, the primary direction aligned with the approximate center of the Milky Way Galaxy, and the fundamental plane (spherical coordin ...

, which places the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

as the pole of the mapping system. The Sun is used instead of the

Galactic Center The Galactic Center is the barycenter of the Milky Way and a corresponding point on the rotational axis of the galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a ...

for practical reasons since all astronomical observations (by

human Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

s) to date have been based on

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

or within the

Solar System The Solar SystemCapitalization 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 "Sola ...

Delineation

Quadrants are described using ordinals—for example, "1st galactic quadrant", "second galactic quadrant", or "third quadrant of the Galaxy".M. Lampton ''et al''
An All-Sky Catalog of Faint Extreme Ultraviolet Sources
''The Astrophysical Journal Supplement Series''. 1997 Viewing from the

north galactic pole The galactic coordinate system is a celestial coordinate system in spherical coordinates, with the Sun as its center, the primary direction aligned with the approximate center of the Milky Way Galaxy, and the fundamental plane (spherical coordin ...

with 0 degrees (°) as the ray that runs starting from the Sun and through the galactic center, the quadrants are as follows (where is galactic longitude): * 1st galactic quadrant – 0° ≤ ≤ 90° * 2nd galactic quadrant – 90° ≤ ≤ 180° * 3rd galactic quadrant – 180° ≤ ≤ 270° * 4th galactic quadrant – 270° ≤ ≤ 360°

Constellations grouped by galactic quadrants

2MASS LSS chart-NEW Nasa-added quadrants

Visibility of each quadrant

Due to the orientation of the Earth to the rest of the galaxy, the 2nd galactic quadrant is primarily only visible from the

northern hemisphere The Northern Hemisphere is the half of Earth that is north of the equator. For other planets in the Solar System, north is defined by humans as being in the same celestial sphere, celestial hemisphere relative to the invariable plane of the Solar ...

while the 4th galactic quadrant is mostly only visible from the southern hemisphere. Thus, it is usually more practical for amateur stargazers to use the celestial quadrants. Nonetheless, cooperating or international astronomical organizations are not so bound by the Earth's

horizon The horizon is the apparent curve that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This curve divides all viewing directions based on whethe ...

. Based on a view from Earth, one may look towards major

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

s for a rough sense of where the borders of the quadrants are: (Note: by drawing a line through the following, one can also approximate the galactic equator.) * For 0°, look towards the Sagittarius constellation. (The galactic center) * For 90°, look towards the Cygnus constellation. * For 180°, look towards the Auriga constellation. (The galactic anticenter) * For 270°, look towards the Vela constellation.

Traditional fourfold divisions of the skies

A long tradition of dividing the visible skies into four precedes the modern definitions of four galactic quadrants. Ancient Mesopotamian formulae spoke of "the four corners of the universe" and of "the heaven's four corners", and the Biblical

Book of Jeremiah The Book of Jeremiah () is the second of the Latter Prophets in the Hebrew Bible, and the second of the Prophets in the Christian Old Testament. The superscription at chapter Jeremiah 1#Superscription, Jeremiah 1:1–3 identifies the book as "th ...

echoes this phraseology: "And upon Elam will I bring the four winds from the four quarters of heaven" (Jeremiah, 49:36).

Astrology Astrology is a range of Divination, divinatory practices, recognized as pseudoscientific since the 18th century, that propose that information about human affairs and terrestrial events may be discerned by studying the apparent positions ...

too uses quadrant systems to divide up its stars of interest. The astronomy of the location of

s sees each of the Northern and Southern

celestial hemisphere In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphere, ...

s divided into four quadrants.

In fiction

''Star Trek''

"Galactic quadrants" within ''

Star Trek ''Star Trek'' is an American science fiction media franchise created by Gene Roddenberry, which began with the Star Trek: The Original Series, series of the same name and became a worldwide Popular culture, pop-culture Cultural influence of ...

'' are based around a meridian that runs from the center of the Galaxy through Earth's

, which is not unlike the system used by astronomers. However, rather than have the

perpendicular In geometry, two geometric objects are perpendicular if they intersect at right angles, i.e. at an angle of 90 degrees or π/2 radians. The condition of perpendicularity may be represented graphically using the '' perpendicular symbol'', � ...

axis An axis (: axes) may refer to: Mathematics *A specific line (often a directed line) that plays an important role in some contexts. In particular: ** Coordinate axis of a coordinate system *** ''x''-axis, ''y''-axis, ''z''-axis, common names ...

run through the Sun, as is done in astronomy, the ''Star Trek'' version runs the axis through the galactic center. In that sense, the ''Star Trek'' quadrant system is less

geocentric In astronomy, the geocentric model (also known as geocentrism, often exemplified specifically by the Ptolemaic system) is a superseded description of the Universe with Earth at the center. Under most geocentric models, the Sun, Moon, stars, an ...

as a cartographical system than the standard. Also, rather than use ordinals, ''Star Trek'' designates them by the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

letters

Alpha Alpha (uppercase , lowercase ) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician letter ''aleph'' , whose name comes from the West Semitic word for ' ...

Beta Beta (, ; uppercase , lowercase , or cursive ; or ) is the second letter of the Greek alphabet. In the system of Greek numerals, it has a value of 2. In Ancient Greek, beta represented the voiced bilabial plosive . In Modern Greek, it represe ...

Gamma Gamma (; uppercase , lowercase ; ) is the third letter of the Greek alphabet. In the system of Greek numerals it has a value of 3. In Ancient Greek, the letter gamma represented a voiced velar stop . In Modern Greek, this letter normally repr ...

, and

Delta Delta commonly refers to: * Delta (letter) (Δ or δ), the fourth letter of the Greek alphabet * D (NATO phonetic alphabet: "Delta"), the fourth letter in the Latin alphabet * River delta, at a river mouth * Delta Air Lines, a major US carrier ...

. The Canadian Galactic Plane Survey (CGPS) created a

radio Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connec ...

map of the Galaxy based on ''Star Trek''s quadrants, joking that "the CGPS is primarily concerned with Cardassians, while the SGPS (Southern Galactic Plane Survey) focuses on

Romulans The Romulans () are an extraterrestrials in fiction, extraterrestrial race in the American science fiction franchise ''Star Trek''. Their adopted home world is Romulus, and within the same star system they have settled a sister planet Remus. Their ...

''Star Wars''

"Galactic quadrants" within ''

Star Wars ''Star Wars'' is an American epic film, epic space opera media franchise created by George Lucas, which began with the Star Wars (film), eponymous 1977 film and Cultural impact of Star Wars, quickly became a worldwide popular culture, pop cu ...

'' canon astrography map depicts a top-down view of the galactic disk, with "Quadrant A" (i.e. "north") as the side of the galactic center that Coruscant is located on. As the capital planet of the Republic and later the Empire, Coruscant is used as the reference point for galactic astronomy, set at XYZ coordinates 0-0-0. Standardized galactic time measurements are also based on Coruscant's local solar day and year.

''Warhammer 40,000''

The Imperium of Man's territory in the Milky Way Galaxy in ''

Warhammer 40,000 ''Warhammer 40,000'' is a miniature wargame produced by Games Workshop. It is the most popular miniature wargame in the world, and is particularly popular in the United Kingdom. The first edition of the rulebook was published in September 1987 ...

'' is divided into five zones, known as "segmentae".Segmentum
Warhammer 40k - Lexicanum Navigation in the Milky Way is also identified with cardinal directions, indicating distance from the Sol System: for example, Ultima Segmentum, the largest segmentum in the Imperium of Man, is located to the galactic east of the Sol System. The 0° "north" in Imperial maps does not correspond to the 0° in the real-world.

References

External links

Milky Way Explorer
{{DEFAULTSORT:Galactic Quadrant Astronomical coordinate systems Milky Way Orientation (geometry)