At all times, the entire Southern Sky is visible from the geographic South Pole; less of the Southern Sky is visible the further north the observer is located. The northern counterpart is the northern celestial hemisphere.
In the context of astronomical discussions or writing about celestial mapping, it may also simply then be referred to as the Southern 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.[according to whom?] 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 should not be confused with descriptions of the terrestrialhemispheres of Earth itself.[according to whom?]
Observation
Chart of the southern constellations from declination –40° to the south celestial pole by the Jesuit missionary François Noël published in Acta Eruditorum, 1711.
The brightest star in the night sky is located in the southern celestial hemisphere and is larger than the Sun. Sirius in the constellation of Canis Major has the brightest apparent magnitude of −1.46; it has a radius twice that of the Sun and is 8.6 light-years away. Canopus and the next fixed star α Centauri, 4.2 light-years away, are also located in the Southern Sky, having declinations around −60°; too close to the south celestial pole for either to be visible from Central Europe.[1]
Of the 88 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]
