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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 parallel to an approximation of the galactic plane but offset to its north. It uses the right-handed convention, meaning that coordinates are positive toward the north and toward the east in the fundamental plane.^[1]

Spherical coordinates

Galactic longitude

Longitude (symbol $l$ ) measures the angular distance of an object eastward along the galactic equator from the Galactic Center. Analogous to terrestrial longitude, galactic longitude is usually measured in degrees (°).

Galactic latitude

Latitude (symbol $b$ ) measures the angle of an object northward of the galactic equator (or midplane) as viewed from Earth. Analogous to terrestrial latitude, galactic latitude is usually measured in degrees (°).

Definition

The first galactic coordinate system was used by William Herschel in 1785. A number of different coordinate systems, each differing by a few degrees, were used until 1932, when Lund Observatory assembled a set of conversion tables that defined a standard galactic coordinate system based on a galactic north pole at RA 12^h 40^m, dec +28° (in the B1900.0 epoch convention) and a 0° longitude at the point where the galactic plane and equatorial plane intersected.^[1]

In 1958, the International Astronomical Union (IAU) defined the galactic coordinate system in reference to radio observations of galactic neutral hydrogen through the hydrogen line, changing the definition of the Galactic longitude by 32° and the latitude by 1.5°.^[1] In the equatorial coordinate system, for equinox and equator of 1950.0, the north galactic pole is defined at right ascension 12^h 49^m, declination +27.4°, in the constellation Coma Berenices, with a probable error of ±0.1°.^[2] Longitude 0° is the great semicircle that originates from this point along the line in position angle 123° with respect to the equatorial pole. The galactic longitude increases in the same direction as right ascension. Galactic latitude is positive towards the north galactic pole, with a plane passing through the Sun and parallel to the galactic equator being 0°, whilst the poles are ±90°.^[3] Based on this definition, the galactic poles and equator can be found from spherical trigonometry and can be precessed to other epochs; see the table.

J2000.0 equatorial coordinates approximating the galactic reference points^[1]

Right ascension

Declination

Constellation

North Pole
+90° latitude

12^h 51.4^m

+27.13°

Coma Berenices
(near 31 Com)

South Pole
−90° latitude

0^h 51.4^m

−27.13°

Sculptor
(near NGC 288)

Center
0° longitude

17^h 45.6^m

−28.94°

Sagittarius
(in Sagittarius A)

Anticenter
180° longitude

5^h 45.6^m

+28.94°

Auriga
(near HIP 27180)

Galactic north	Galactic south	Galactic center

The IAU recommended that during the transition period from the old, pre-1958 system to the new, the old longitude and latitude should be designated $l I$ and $b I$ while the new should be designated $l II$ and $b II$ .^[3] This convention is occasionally seen.^[4]

Radio source Sagittarius A*, which is the best physical marker of the true Galactic Center, is located at 17^h 45^m 40.0409^s, −29° 00′ 28.118″ (J2000).^[2] Rounded to the same number of digits as the table, 17^h 45.7^m, −29.01° (J2000), there is an offset of about 0.07° from the defined coordinate center, well within the 1958 error estimate of ±0.1°. Due to the Sun's position, which currently lies 56.75±6.20 ly north of the midplane, and the heliocentric definition adopted by the IAU, the galactic coordinates of Sgr A* are latitude +0° 07′ 12″ south, longitude 0° 04′ 06″. Since as defined the galactic coordinate system does not rotate with time, Sgr A* is actually decreasing in longitude at the rate of galactic rotation at the sun, $Ω$ , approximately 5.7 milliarcseconds per year (see Oort constants).

Conversion between equatorial and galactic coordinates

An object's location expressed in the equatorial coordinate system can be transformed into the galactic coordinate system. In these equations, $α$ is right ascension, $δ$ is declination. NGP refers to the coordinate values of the north galactic pole and NCP to those of the north celestial pole.^[5]

{\begin{aligned}\sin(b)&=\sin(\delta _{\text{NGP}})\sin(\delta )+\cos(\delta _{\text{NGP}})\cos(\delta )\cos(\alpha -\alpha _{\text{NGP}})\\\cos(b)\sin(l_{\text{NCP}}-l)&=\cos(\delta )\sin(\alpha -\alpha _{\text{NGP}})\\\cos(b)\cos(l_{\text{NCP}}-l)&=\cos(\delta _{\text{NGP}})\sin(\delta )-\sin(\delta _{\text{NGP}})\cos(\delta )\cos(\alpha -\alpha _{\text{NGP}})\end{aligned}}

The reverse (galactic to equatorial) can also be accomplished with the following conversion formulas.

{\begin{aligned}\sin(\delta )&=\sin(\delta _{\text{NGP}})\sin(b)+\cos(\delta _{\text{NGP}})\cos(b)\cos(l_{\text{NCP}}-l)\\\cos(\delta )\sin(\alpha -\alpha _{\text{NGP}})&=\cos(b)\sin(l_{\text{NCP}}-l)\\\cos(\delta )\cos(\alpha -\alpha _{\text{NGP}})&=\cos(\delta _{\text{NGP}})\sin(b)-\sin(\delta _{\text{NGP}})\cos(b)\cos(l_{\text{NCP}}-l)\end{aligned}}

Where:

\alpha _{\text{NGP}}=12^{h}51.4^{m}\qquad \delta _{\text{NGP}}=27.13^{\circ }\qquad l_{\text{NCP}}=122.93314^{\circ }

Rectangular coordinates

In some applications use is made of rectangular coordinates based on galactic longitude and latitude and distance. In some work regarding the distant past or future the galactic coordinate system is taken as rotating so that the $x$ -axis always goes to the centre of the galaxy.^[6]

There are two major rectangular variations of galactic coordinates, commonly used for computing space velocities of galactic objects. In these systems the $xyz$ -axes are designated $UVW$ , but the definitions vary by author. In one system, the $U$ axis is directed toward the Galactic Center ( $l$ = 0°), and it is a right-handed system (positive towards the east and towards the north galactic pole); in the other, the $U$ axis is directed toward the galactic anticenter ( $l$ = 180°), and it is a left-handed system (positive towards the east and towards the north galactic pole).^[7]

In the constellations

The galactic equator runs through the following constellations:^[8]

References

^ ^a ^b ^c ^d Blaauw, A.; Gum, C.S.; Pawsey, J.L.; Westerhout, G. (1960). "The new IAU system of galactic coordinates (1958 revision)". Monthly Notices of the Royal Astronomical Society. 121 (2): 123. Bibcode:1960MNRAS.121..123B. doi:10.1093/mnras/121.2.123.
^ ^a ^b Reid, M.J.; Brunthaler, A. (2004). "The Proper Motion of Sagittarius A*". The Astrophysical Journal. 616 (2): 874, 883. arXiv:astro-ph/0408107. Bibcode:2004ApJ...616..872R. doi:10.1086/424960. S2CID 16568545.
^ ^a ^b James Binney, Michael Merrifield (1998). Galactic Astronomy. Princeton University Press. pp. 30–31. ISBN 0-691-02565-7.
^ For example in Kogut, A.; et al. (1993). "Dipole Anisotropy in the COBE Differential Microwave Radiometers First-Year Sky Maps". Astrophysical Journal. 419: 1. arXiv:astro-ph/9312056. Bibcode:1993ApJ...419....1K. doi:10.1086/173453.
^ Carroll, Bradley; Ostlie, Dale (2007). An Introduction to Modern Astrophysics (2nd ed.). Pearson Addison-Wesley. pp. 900–901. ISBN 978-0805304022.
^ For example Bobylev, Vadim V. (March 2010). "Searching for Stars Closely Encountering with the Solar System". Astronomy Letters. 36 (3): 220–226. arXiv:1003.2160. Bibcode:2010AstL...36..220B. doi:10.1134/S1063773710030060. S2CID 118374161.
^ Johnson, Dean R.H.; Soderblom, David R. (1987). "Calculating galactic space velocities and their uncertainties, with an application to the Ursa Major group". Astronomical Journal. 93: 864. Bibcode:1987AJ.....93..864J. doi:10.1086/114370.
^ "SEDS Milky Way Constellations".

External links

Universal coordinate converter.
Galactic Coordinate System - Wolfram Demonstration
Galactic coordinates, The Internet Encyclopedia of Science
Fiona Vincent, Positional Astronomy: Galactic coordinates Archived 2012-09-10 at the Wayback Machine, University of St Andrews
An Atlas of the Universe

[Blaauwetal-1] Blaauw, A.; Gum, C.S.; Pawsey, J.L.; Westerhout, G. (1960). "The new IAU system of galactic coordinates (1958 revision)". Monthly Notices of the Royal Astronomical Society. 121 (2): 123. Bibcode:1960MNRAS.121..123B. doi:10.1093/mnras/121.2.123.

[Reidetal-2] Reid, M.J.; Brunthaler, A. (2004). "The Proper Motion of Sagittarius A*". The Astrophysical Journal. 616 (2): 874, 883. arXiv:astro-ph/0408107. Bibcode:2004ApJ...616..872R. doi:10.1086/424960. S2CID 16568545.

[Binney-3] James Binney, Michael Merrifield (1998). Galactic Astronomy. Princeton University Press. pp. 30–31. ISBN 0-691-02565-7.

[4] For example in Kogut, A.; et al. (1993). "Dipole Anisotropy in the COBE Differential Microwave Radiometers First-Year Sky Maps". Astrophysical Journal. 419: 1. arXiv:astro-ph/9312056. Bibcode:1993ApJ...419....1K. doi:10.1086/173453.

[5] Carroll, Bradley; Ostlie, Dale (2007). An Introduction to Modern Astrophysics (2nd ed.). Pearson Addison-Wesley. pp. 900–901. ISBN 978-0805304022.

[6] For example Bobylev, Vadim V. (March 2010). "Searching for Stars Closely Encountering with the Solar System". Astronomy Letters. 36 (3): 220–226. arXiv:1003.2160. Bibcode:2010AstL...36..220B. doi:10.1134/S1063773710030060. S2CID 118374161.

[Johnson-7] Johnson, Dean R.H.; Soderblom, David R. (1987). "Calculating galactic space velocities and their uncertainties, with an application to the Ursa Major group". Astronomical Journal. 93: 864. Bibcode:1987AJ.....93..864J. doi:10.1086/114370.

[SEDS-8] "SEDS Milky Way Constellations".

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

@@ Line 1: / Line 1: @@
-{{short description|A celestial coordinate system in spherical coordinates, with the Sun as its center}}
+{{short description|Celestial coordinate system in spherical coordinates, with the Sun as its center}}
 <!-- linked from redirects [[North galactic pole]] and [[South galactic pole]] -->
-[[File:Artist's impression of the Milky Way (updated - annotated).jpg|thumb|Artist's depiction of the Milky Way galaxy, showing the galactic longitude relative to the [[Galactic Center]]]]
+[[File:Artist's impression of the Milky Way (updated - annotated).jpg|thumb|upright=1.3|Artist's depiction of the Milky Way Galaxy showing the origin and orientation of galactic longitude. The galactic longitude ({{math|''l''}}) runs from the Sun upwards in the image through the center of the galaxy. The galactic latitude ({{math|''b''}}) is perpendicular to the image (i.e. coming out of the image) and also centered on the Sun.]]
-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 coordinates)|fundamental plane]] parallel to an approximation of the [[galactic plane]] but offset to its north. It uses the [[Right-hand rule|right-handed convention]], meaning that coordinates are positive toward the north and toward the east in the [[fundamental plane (spherical coordinates)|fundamental plane]].<ref name="Blaauwetal" />
+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 coordinates)|fundamental plane]] parallel to an approximation of the [[galactic plane]] but offset to its north. It uses the [[Right-hand rule|right-handed convention]], meaning that coordinates are positive toward the north and toward the east in the [[fundamental plane (spherical coordinates)|fundamental plane]].<ref name="Blaauwetal" />
+==Spherical coordinates==
-== Galactic longitude ==
+=== Galactic longitude ===
 [[File:Galactic coordinates.JPG|thumb| The galactic coordinates use the [[Sun]] as the origin. Galactic longitude ({{math|''l''}}) is measured with primary direction from the Sun to the center of the galaxy in the galactic plane, while the galactic latitude ({{math|''b''}}) measures the [[angle]] of the object above the [[galactic plane]].]]
-Longitude (symbol {{math|''l''}}) measures the [[angle|angular distance]] of an object eastward along the galactic equator from the galactic center. Analogous to terrestrial [[longitude]], galactic longitude is usually measured in degrees (°).
+Longitude (symbol {{math|''l''}}) measures the [[angle|angular distance]] of an object eastward along the galactic equator from the Galactic Center. Analogous to terrestrial [[longitude]], galactic longitude is usually measured in degrees (°).
-== Galactic latitude ==
+=== Galactic latitude ===
-Latitude (symbol {{math|''b''}}) measures the [[angle]] of an object north or south of the galactic equator (or midplane) as viewed from Earth; positive to the north, negative to the south. For example, the north galactic pole has a latitude of +90°. Analogous to terrestrial [[latitude]], galactic latitude is usually measured in degrees (°).
+Latitude (symbol {{math|''b''}}) measures the [[angle]] of an object northward of the galactic equator (or midplane) as viewed from Earth. Analogous to terrestrial [[latitude]], galactic latitude is usually measured in degrees (°).
 == Definition ==
@@ Line 17: / Line 18: @@
 The first galactic coordinate system was used by [[William Herschel]] in 1785. A number of different coordinate systems, each differing by a few degrees, were used until 1932, when [[Lund Observatory]] assembled a set of conversion tables that defined a standard galactic coordinate system based on a galactic north pole at [[right ascension|RA]] {{nowrap|12<sup>h</sup>&thinsp;40<sup>m</sup>}}, [[declination|dec]] +28° (in the [[B1900.0]] epoch convention) and a 0° longitude at the point where the [[galactic plane]] and [[equatorial plane]] intersected.<ref name="Blaauwetal" />
+In 1958, the [[International Astronomical Union]] (IAU) defined the galactic coordinate system in reference to radio observations of galactic neutral [[hydrogen]] through the [[hydrogen line]], changing the definition of the Galactic longitude by 32° and the latitude by 1.5°.<ref name="Blaauwetal" /> In the [[equatorial coordinate system]], for [[Epoch (astronomy)|equinox and equator of 1950.0]], the north galactic pole is defined at [[right ascension]] {{nowrap|12<sup>h</sup>&thinsp;49<sup>m</sup>}}, [[declination]] +27.4°, in the constellation [[Coma Berenices]], with a probable error of ±0.1°.<ref name="Reidetal" /> Longitude 0° is the great semicircle that originates from this point along the line in [[position angle]] 123° with respect to the [[Celestial pole|equatorial pole]]. The galactic longitude increases in the same direction as right ascension. Galactic latitude is positive towards the north galactic pole, with a plane passing through the Sun and parallel to the galactic equator being 0°, whilst the poles are ±90°.<ref name="Binney" /> Based on this definition, the galactic poles and equator can be found from [[spherical trigonometry]] and can be [[axial precession|precessed]] to other [[Epoch (astronomy)|epochs]]; see the table.
 {| class="wikitable" style="float: right;"
-|+'''[[equatorial coordinate system|Equatorial coordinates]] [[epoch (astronomy)|J2000.0]] of galactic reference points'''<ref name="Blaauwetal"/>
+|+'''[[epoch (astronomy)|J2000.0]] [[equatorial coordinate system|equatorial coordinates]] approximating the galactic reference points'''<ref name="Blaauwetal"/>
 | style="background:#e9d66b;"| &nbsp;
 |  style="text-align:center; background:#e9d66b;"| '''[[Right ascension]]'''
@@ Line 42: / Line 46: @@
 | 5<sup>h</sup>&thinsp;45.6<sup>m</sup>
 | +28.94°
-| [[Auriga (constellation)|Auriga]]<br/><small>(near [[Hipparcos|HIP]] 27088)</small>
+| [[Auriga (constellation)|Auriga]]<br/><small>(near [[Hipparcos|HIP]] 27180)</small>
 |-
 |colspan=4|
@@ Line 52: / Line 56: @@
 |}
+[[File:2MASS LSS chart-NEW Nasa-added quadrants.jpg|thumb|Approx galactic quadrants (NGQ/SGQ, 1–4) indicated, along with differentiating Galactic Plane (containing galactic centre) and the Galactic Coordinates Plane (containing our sun / solar system)]]
-In 1958, the [[International Astronomical Union]] (IAU) defined the galactic coordinate system in reference to radio observations of galactic neutral [[hydrogen]] through the [[hydrogen line]], changing the definition of the Galactic longitude by 32° and the latitude by 1.5°.<ref name="Blaauwetal" /> In the [[equatorial coordinate system]], for [[Epoch (astronomy)|equinox and equator of 1950.0]], the north galactic pole is defined at [[right ascension]] {{nowrap|12<sup>h</sup>&thinsp;49<sup>m</sup>}}, [[declination]] +27.4°, in the constellation [[Coma Berenices]], with a probable error of ±0.1°.<ref name="Reidetal" /> Longitude 0° is the great semicircle that originates from this point along the line in [[position angle]] 123° with respect to the [[Celestial pole|equatorial pole]]. The galactic longitude increases in the same direction as right ascension. Galactic latitude is positive towards the north galactic pole, with a plane passing through the Sun and parallel to the galactic equator being 0°, whilst the poles are ±90°.<ref name="Binney" /> Based on this definition, the galactic poles and equator can be found from [[spherical trigonometry]] and can be [[axial precession|precessed]] to other [[Epoch (astronomy)|epochs]]; see the table.
 The IAU recommended that during the transition period from the old, pre-1958 system to the new, the old longitude and latitude should be designated {{math|''l''{{isup|I}}}} and {{math|''b''{{isup|I}}}} while the new should be designated {{math|''l''{{isup|II}}}} and {{math|''b''{{isup|II}}}}.<ref name=Binney/> This convention is occasionally seen.<ref>For example in {{Cite journal |last=Kogut |first=A. |date=1993 |title=Dipole Anisotropy in the COBE Differential Microwave Radiometers First-Year Sky Maps |journal=[[Astrophysical Journal]] |volume=419 |page=1 |arxiv=astro-ph/9312056 |doi=10.1086/173453|bibcode = 1993ApJ...419....1K |display-authors=etal}}</ref>
-[[radio astronomy|Radio source]] [[Sagittarius A*]], which is the best physical marker of the true [[galactic center]], is located at {{nowrap|17<sup>h</sup>&thinsp;45<sup>m</sup>&thinsp;40.0409<sup>s</sup>}}, {{nowrap|−29°&thinsp;00′&thinsp;28.118″}} (J2000).<ref name="Reidetal"/> Rounded to the same number of digits as the table, {{nowrap|17<sup>h</sup>&thinsp;45.7<sup>m</sup>}}, −29.01° (J2000), there is an offset of about 0.07° from the defined coordinate center, well within the 1958 error estimate of ±0.1°. Due to the Sun's position, which currently lies {{val|56.75|6.20|ul=ly}} north of the midplane, and the heliocentric definition adopted by the IAU, the galactic coordinates of Sgr&nbsp;A* are latitude {{nowrap|+0°&thinsp;07′&thinsp;12″}} south, longitude {{nowrap|0°&thinsp;04′&thinsp;06″}}. Since as defined the galactic coordinate system does not rotate with time, Sgr&nbsp;A* is actually decreasing in longitude at the rate of galactic rotation at the sun, {{mvar|Ω}}, approximately 5.7 [[milliarcsecond]]s per year (see [[Oort constants]]).
+[[radio astronomy|Radio source]] [[Sagittarius A*]], which is the best physical marker of the true [[Galactic Center]], is located at {{nowrap|17<sup>h</sup>&thinsp;45<sup>m</sup>&thinsp;40.0409<sup>s</sup>}}, {{nowrap|−29°&thinsp;00′&thinsp;28.118″}} (J2000).<ref name="Reidetal"/> Rounded to the same number of digits as the table, {{nowrap|17<sup>h</sup>&thinsp;45.7<sup>m</sup>}}, −29.01° (J2000), there is an offset of about 0.07° from the defined coordinate center, well within the 1958 error estimate of ±0.1°. Due to the Sun's position, which currently lies {{val|56.75|6.20|ul=ly}} north of the midplane, and the heliocentric definition adopted by the IAU, the galactic coordinates of Sgr&nbsp;A* are latitude {{nowrap|+0°&thinsp;07′&thinsp;12″}} south, longitude {{nowrap|0°&thinsp;04′&thinsp;06″}}. Since as defined the galactic coordinate system does not rotate with time, Sgr&nbsp;A* is actually decreasing in longitude at the rate of galactic rotation at the sun, {{mvar|Ω}}, approximately 5.7 [[milliarcsecond]]s per year (see [[Oort constants]]).
-==Conversion between Equatorial and Galactic Coordinates==
+==Conversion between equatorial and galactic coordinates==
-An object's location expressed in the [[equatorial coordinate system]] can be transformed into the galactic coordinate system. In these equations, {{math|''α''}} is [[right ascension]], {{math|''δ''}} is [[declination]]. NGP refers to the coordinate values of the north galactic pole and NCP to those of the north celestial pole.<ref>{{cite book |last1=Carroll |first1=Bradley |last2=Ostlie |first2=Dale |title=An Introduction to Modern Astrophysics |publisher=Pearson Addison-Wesley |isbn=978-0805304022 |page=1054-1056 |edition=2nd}}</ref>
+An object's location expressed in the [[equatorial coordinate system]] can be transformed into the galactic coordinate system. In these equations, {{math|''α''}} is [[right ascension]], {{math|''δ''}} is [[declination]]. NGP refers to the coordinate values of the north galactic pole and NCP to those of the north celestial pole.<ref>{{cite book |last1=Carroll |first1=Bradley |last2=Ostlie |first2=Dale |title=An Introduction to Modern Astrophysics |year=2007 |publisher=Pearson Addison-Wesley |isbn=978-0805304022 |pages=900–901 |edition=2nd}}</ref>
 :<math>
@@ Line 78: / Line 82: @@
 </math>
+Where:
-==Rectangular coordinates==
-In some applications use is made of rectangular coordinates based on galactic longitude and latitude and distance. In some work regarding the distant past or future the galactic coordinate system is taken as rotating so that the {{math|''x''}}-axis always goes to the centre of the galaxy.<ref>For example {{cite journal |last=Bobylev |first=Vadim V. |authorlink= | date=March 2010 |title=Searching for Stars Closely Encountering with the Solar System |journal=Astronomy Letters |volume=36 |issue=3 |pages=220–226 |doi=10.1134/S1063773710030060 |arxiv=1003.2160 |bibcode=2010AstL...36..220B}}</ref>
+:<math>\alpha_\text{NGP}=12^h 51.4^m \qquad \delta_\text{NGP}=27.13^{\circ} \qquad l_\text{NCP}=122.93314^{\circ}</math>
-There are two major [[Cartesian coordinate system|rectangular]] variations of galactic coordinates, commonly used for computing space velocities of galactic objects. In these systems the {{math|''xyz''}}-axes are designated {{math|''UVW''}}, but the definitions vary by author. In one system, the {{math|''U''}} axis is directed toward the galactic center ({{math|''l''}} = 0°), and it is a [[Right-hand rule|right-handed]] system (positive towards the east and towards the north galactic pole); in the other, the {{math|''U''}} axis is directed toward the galactic anticenter ({{math|''l''}} = 180°), and it is a left-handed system (positive towards the east and towards the north galactic pole).<ref name="Johnson" />
+==Rectangular coordinates==
-==In the constellations==
+In some applications use is made of rectangular coordinates based on galactic longitude and latitude and distance. In some work regarding the distant past or future the galactic coordinate system is taken as rotating so that the {{math|''x''}}-axis always goes to the centre of the galaxy.<ref>For example {{cite journal |last=Bobylev |first=Vadim V. | date=March 2010 |title=Searching for Stars Closely Encountering with the Solar System |journal=Astronomy Letters |volume=36 |issue=3 |pages=220–226 |doi=10.1134/S1063773710030060 |arxiv=1003.2160 |bibcode=2010AstL...36..220B|s2cid=118374161 }}</ref>
+There are two major [[Cartesian coordinate system|rectangular]] variations of galactic coordinates, commonly used for computing space velocities of galactic objects. In these systems the {{math|''xyz''}}-axes are designated {{math|''UVW''}}, but the definitions vary by author. In one system, the {{math|''U''}} axis is directed toward the Galactic Center ({{math|''l''}} = 0°), and it is a [[Right-hand rule|right-handed]] system (positive towards the east and towards the north galactic pole); in the other, the {{math|''U''}} axis is directed toward the galactic anticenter ({{math|''l''}} = 180°), and it is a left-handed system (positive towards the east and towards the north galactic pole).<ref name="Johnson" />
 [[Image:Milky Way infrared.jpg|thumb|250px|The [[anisotropy]] of the star density in the night sky makes the galactic coordinate system very useful for coordinating surveys, both those that require high densities of stars at low galactic latitudes, and those that require a low density of stars at high galactic latitudes. For this image the [[Mollweide projection]] has been applied, typical in maps using galactic coordinates.]]
+==In the constellations==
 The galactic equator runs through the following [[constellation]]s:<ref name="SEDS" />
@@ Line 104: / Line 112: @@
 *[[Gemini (constellation)|Gemini]]
 *[[Orion (constellation)|Orion]]
-*[[Monoceros]]
+*[[Monoceros (constellation)|Monoceros]]
 *[[Canis Major]]
 *[[Puppis]]
@@ Line 122: / Line 130: @@
 * {{annotated link|Galactic quadrant}}
 * {{annotated link|Supergalactic coordinate system}}
-* {{annotated link|Celestial coordinate system}}
+* {{annotated link|Astronomical coordinate systems}}
 * {{annotated link|Galaxy formation and evolution}}
 * {{annotated link|Milky Way}}
@@ Line 129: / Line 137: @@
 {{reflist|20em|refs=
 <ref name="Blaauwetal">{{cite journal |title=The new IAU system of galactic coordinates (1958 revision) |first1=A. |last1=Blaauw
-|last2=Gum |first2=C.S. |last3=Pawsey |first3=J.L. |last4=Westerhout |first4=G. |date=1960 |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=121 |number=2 |page=123 |bibcode = 1960MNRAS.121..123B |doi=10.1093/mnras/121.2.123}}</ref>
+|last2=Gum |first2=C.S. |last3=Pawsey |first3=J.L. |last4=Westerhout |first4=G. |date=1960 |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=121 |number=2 |page=123 |bibcode = 1960MNRAS.121..123B |doi=10.1093/mnras/121.2.123|doi-access=free }}</ref>
-<ref name="Reidetal">{{cite journal | last1=Reid | first1=M.J. | last2=Brunthaler | first2=A. | title=The Proper Motion of Sagittarius A* | journal=The Astrophysical Journal | publisher=The American Astronomical Society | volume=616 | issue=2 | pages=874, 883 | date=2004 | bibcode=2004ApJ...616..872R|arxiv = astro-ph/0408107 |doi = 10.1086/424960 }}</ref>
+<ref name="Reidetal">{{cite journal | last1=Reid | first1=M.J. | last2=Brunthaler | first2=A. | title=The Proper Motion of Sagittarius A* | journal=The Astrophysical Journal | volume=616 | issue=2 | pages=874, 883 | date=2004 | bibcode=2004ApJ...616..872R|arxiv = astro-ph/0408107 |doi = 10.1086/424960 | s2cid=16568545 }}</ref>
-<ref name="Binney">{{cite book |title=Galactic Astronomy |author=James Binney, Michael Merrifield |url=https://books.google.com/?id=arYYRoYjKacC&pg=PA675&dq=rotation+%22proper+motion%22+galaxy+OR+galactic |pages= 30–31 |isbn=0-691-02565-7 |date=1998 |publisher=[[Princeton University Press]]}}</ref>
+<ref name="Binney">{{cite book |title=Galactic Astronomy |author=James Binney, Michael Merrifield |url=https://books.google.com/books?id=arYYRoYjKacC&q=rotation+%22proper+motion%22+galaxy+OR+galactic&pg=PA675 |pages= 30–31 |isbn=0-691-02565-7 |date=1998 |publisher=[[Princeton University Press]]}}</ref>
-<ref name="Johnson">{{cite journal |title=Calculating galactic space velocities and their uncertainties, with an application to the Ursa Major group |last1=Johnson |first1=Dean R.H. |last2=Soderblom |first2=David R. |date=1987 |work=Astronomical Journal |volume=93 |page=864|bibcode = 1987AJ.....93..864J |doi = 10.1086/114370}}</ref>
+<ref name="Johnson">{{cite journal |title=Calculating galactic space velocities and their uncertainties, with an application to the Ursa Major group |last1=Johnson |first1=Dean R.H. |last2=Soderblom |first2=David R. |date=1987 |journal=Astronomical Journal |volume=93 |page=864|bibcode = 1987AJ.....93..864J |doi = 10.1086/114370}}</ref>
 <ref name="SEDS">{{cite web | url=http://messier.seds.org/more/mw_con.html | title=SEDS Milky Way Constellations}}</ref>
 }}
@@ Line 140: / Line 148: @@
 * [http://demonstrations.wolfram.com/GalacticCoordinateSystem/  Galactic Coordinate System - Wolfram Demonstration]
 * [https://www.daviddarling.info/encyclopedia/C/coordinate.html#galactic_coordinates Galactic coordinates], The [[Internet Encyclopedia of Science]]
-* Fiona Vincent, [http://star-www.st-and.ac.uk/~fv/webnotes/chapter8.htm Positional Astronomy: Galactic coordinates], [[University of St Andrews]]
+* Fiona Vincent, [http://star-www.st-and.ac.uk/~fv/webnotes/chapter8.htm Positional Astronomy: Galactic coordinates] {{Webarchive|url=https://web.archive.org/web/20120910114035/http://star-www.st-and.ac.uk/~fv/webnotes/ |date=2012-09-10 }}, [[University of St Andrews]]
-* [http://www.atlasoftheuniverse.com/ An Atlas of the Universe]
+* [https://web.archive.org/web/20150718054637/http://www.atlasoftheuniverse.com/ An Atlas of the Universe]
 {{Milky Way}}
 {{Galaxy}}
 {{Celestial coordinate systems}}
+{{Portal bar|Stars|Spaceflight|Outer space|Solar System}}
-[[Category:Celestial coordinate system]]
+[[Category:Astronomical coordinate systems]]
 [[Category:Milky Way]]
 [[Category:Orientation (geometry)]]

v t e Galaxies
Morphology	Disc Lenticular barred unbarred Spiral anemic barred flocculent grand design intermediate Magellanic unbarred Dwarf galaxy elliptical irregular spheroidal spiral Elliptical galaxy cD Irregular barred Peculiar Ring Polar
Structure	Active galactic nucleus Bar Bulge Central massive object Galactic Center Dark matter halo Disc Disc galaxy Halo corona Galactic plane Galactic ridge Interstellar medium Protogalaxy Galaxy filament Spiral arm Supermassive black hole Ultramassive
Active nuclei	Blazar LINER Markarian Quasar BL Lacertae object Radio X-shaped DRAGN Relativistic jet Seyfert
Energetic galaxies	Lyman-alpha emitter Lyman-break Luminous infrared ULIRG HLIRG ELIRG Starburst blue compact dwarf pea faint blue Luminous infrared galaxy Hot dust-obscured Green bean galaxy Hanny's Voorwerp Wolf-Rayet galaxy
Low activity	Low surface brightness Ultra diffuse Dark galaxy Red nugget Blue Nugget Dead disk
Interaction	Field Galactic tide Groups and clusters group cluster Brightest cluster galaxy fossil group Interacting merger collision cannibalism Jellyfish Satellite Stellar stream Superclusters Walls Voids and supervoids void galaxy
Lists	Galaxies Galaxies named after people Largest Nearest Polar-ring Ring Spiral Groups and clusters Large quasar groups Quasars List of the most distant astronomical objects Starburst galaxies Superclusters Voids
See also	Extragalactic astronomy Galactic astronomy Galactic coordinate system Galactic habitable zone Galactic magnetic fields Galactic orientation Galactic quadrant Galaxy color–magnitude diagram Galaxy formation and evolution Galaxy rotation curve Gravitational lens Gravitational microlensing Illustris project Intergalactic dust Intergalactic stars Intergalactic travel Population III stars Galaxy X (galaxy)
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