Galactic Longitude

galactic longitude [gə′lak·tik ′län·jə‚tüd]

(astronomy)

Angular distance east of sidereal hour angle 94.4° along the galactic equator; the arc of the galactic equator or the angle at the galactic pole between the great circle through the intersection of the galactic equator and the celestial equator in Sagittarius (SHA 94.4°) and a great circle through the galactic poles, measured eastward from the great circle through SHA 94.4° through 360°.

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Galactic Longitude 

a coordinate in the galactic system of coordinates. Until 1958 galactic longitude was measured from the ascending node of the galactic equator (the old system). In the new system longitudes are calculated from the direction to the center of the Milky Way Galaxy. Galactic longitude in the old system was denoted by l^I and in the new system, by l^II. Now, l without the superscript roman numeral II denotes galactic longitude in the new system.