Galactic Longitude


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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°.

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 lI and in the new system, by lII. Now, l without the superscript roman numeral II denotes galactic longitude in the new system.

References in periodicals archive ?
So if you stand facing west, galactic longitude 90[degrees], which is close to Deneb in Cygnus, will be on your right, near the north point of your horizon.
On your left as you face west, near the south point of the horizon, is galactic longitude 270[degrees].
Its course is clear in the neighborhood of the Sun, and it extends forward (in terms of galactic rotation) to the Cygnus Star Cloud, which lies between galactic longitudes 60[degrees] and 80[degrees].
For observers in the North Temperate Zone, galactic longitude 90[degrees] is nearly straight overhead during early autumn evenings.
Note that these three nearby associations lie at or beyond galactic longitude 90[degrees], the direction of orbital motion of our neighborhood of the galaxy, whereas the more distant Cygnus Star Cloud, where we look down the forward arc of the Orion Cygnus Arm, is between galactic longitudes 80[degrees] and 60[degrees]--in other words, a bit toward the interior of the galaxy.
To get a better perspective on this, look up toward Deneb, in the direction of galactic longitude 90[degrees].
When we look toward galactic longitude 180[degrees], between Auriga and Gemini, we're looking directly away from the galactic center.
At galactic longitude 120 [degrees], hydrogen gas that is mainly in the Perseus arm appears blue-shifted, indicating it is moving toward us.
Just past Deneb close to the North America Nebula we reach 90 [degrees] galactic longitude. Here we are looking at right angles to both the galactic center and anticenter into the depths of the Milky Way's disk along our spiral arm.
Where the interstellar medium was of low density (galactic longitude 225 |degrees~) the shock front expanded relatively quickly.
HEAO-1 did find similar ridgelike emissions along the galactic plane at galactic longitudes greater than 50[deg.].
Recording all dark clouds greater than 0.01 square degree between galactic longitudes 240[degrees] and 360[degrees], they found that only 1.92 percent of the southern sky is obscured, compared with 4.98 percent of the northern sky."