Southern Celestial Hemisphere
For the purpose of celestial mapping, the sky is considered by astronomers as the inside of a sphere divided in two halves by the celestial equator. The Southern Sky or Southern Hemisphere is therefore that half of the celestial sphere that is south of the celestial equator. Even if this one is the ideal projection of the terrestrial equatorial onto the imaginary celestial sphere, the Northern and Southern celestial hemispheres must not be confused with descriptions of the terrestrial hemispheres of Earth itself.
From the South Pole, in good visibility conditions, the southern sky (southern star (s) sky), has over 2,000 fixed stars which can be seen easily with naked eye, while with "aided eye" about 20,000 to 40,000 stars. In large cities, about 300 to 500 stars can be seen depending on the extent of light and air pollution. The farther north, the less is visible to the observer.
The brightest stars are all bigger than our sun. The brightest with -1.5 mag is Sirius in the constellation Great Dog; It has a double sun radius and is 8 light years away. Also Canopus and the next fixed star Toliman (α Centauri) with 4 light years distance are located in the southern sky, but with around 60° southern declination so close to the pole that both can not be observed from Central Europe.
- David Ellyard, Wil Tirion: The Southern Sky Guide. Cambridge Univ. Press, Cambridge 2009, ISBN 978-0-521-71405-1
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