Coordinates given are those of right ascension and declination (based on the celestial equator), which are the equivalents of terrestrial longitude and latitude.
In modern maps, star positions, as well as the positions of other celestial bodies, are always given using right ascension and declination. The coordinates know as celestial longitude and latitude are reserved primarily for computing the positions of the planets. Celestial longitude runs eastward along the ecliptic, and celestial latitude north and south toward the poles of the ecliptic.
Each hour in right ascension is equivalent to 15°. Zero right ascension begins where the celestial equator and the ecliptic intersect - the spring, or vernal, equinox. This is the point at which the Sun crosses the celestial equator and moves into the northern half of the celestial sphere.
Star atlases contain a third set of coordinates (not shown here), which concerns galactic latitude and longitude. These coordinates are based on the Milky Way instead of the ecliptic or the celestial equator, and they are used in studies of the distribution of globular clusters and galaxies.
Observers using a telescope or binoculars will need a star atlas that gives more detail than it is possible to show on the small-scale maps reproduced here. One such widely used atlas is Norton's Star Atlas published by Gall & Inglis, Edinburgh; another consists of the detailed star charts drawn by Wil Tirion and published by the British Astronomical Association. These charts are also available from Enslow Publishers, New Jersey, USA.
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