For the purpose of celestial mapping, the sky is considered as the inside of a sphere divided in two halves by the celestial equator. The northern celestial hemisphere is the northern half of the celestial sphere; that is, it lies north of the celestial equator and appears to rotate westward around a polar axis due to Earth’s rotation. At any given time, the entire Northern Sky is visible from the geographic North Pole, while less of the hemisphere is visible the farther south the observer is located. Many objects within the northern celestial hemisphere can also be viewed from the southern terrestrial hemisphere, depending on the latitude.
