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Thesouthern celestial hemisphere, also called theSouthern Sky, is thesouthern half of thecelestial sphere; that is, it liessouth of thecelestial equator. This arbitrary sphere, on which seeminglyfixed stars formconstellations,appears to rotate westward around apolar axis as the Earthrotates.
At all times, the entire Southern Sky is visible from the geographicSouth Pole; less of the Southern Sky is visible thefurther north the observer is located. The northern counterpart is thenorthern celestial hemisphere.
In the context ofastronomical discussions or writing aboutcelestial mapping, it may also simply then be referred to as the Southern Hemisphere.[citation needed]
For the purpose of celestial mapping, the sky is considered byastronomers as the inside of asphere divided in two halves by thecelestial equator.[according to whom?] The Southern Sky or Southern Hemisphere is, therefore, that half of thecelestial sphere that is south of the celestial equator. Even if this one is the idealprojection of the terrestrial equatorial onto the imaginary celestial sphere, the Northern and Southern celestial hemispheres should not be confused with descriptions of theterrestrialhemispheres ofEarth itself.[according to whom?]
From theSouth Pole, in good visibility conditions, the Southern Sky features over 2,000fixed stars that are easily visible to thenaked eye, while about 20,000 to 40,000 with the aided eye.[citation needed][dubious –discuss] In large cities, about 300 to 500 stars can be seen depending on the extent oflight andair pollution.[citation needed] The farther north, the fewer are visible to the observer.[citation needed]
The brightest star in the night sky is located in the southern celestial hemisphere and is larger than theSun.Sirius in theconstellation of Canis Major has the brightestapparent magnitude of −1.46; it has a radius twicethat of the Sun and is 8.6light-years away.Canopus and the next fixed starα Centauri, 4.2 light-years away, are also located in the Southern Sky, having declinations around −60°; too close to thesouth celestial pole for either to be visible fromCentral Europe.[1] With the pole star being the faint Sigma Octantis
Of the88 modern constellations, 45 are only visible from the Southern celestial hemisphere with 15 other constellations along the equator and have portions on the northern hemisphere. The southern constellations are:[citation needed][2]
The first telescopicchart of the Southern Sky was made by the English astronomerEdmond Halley,[3][4] from the island ofSt Helena in theSouth Atlantic Ocean and published by him in 1678.[5]
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