The northern celestial hemisphere, also called the Northern Sky, is the northern half of the celestial sphere; that is, it lies north of the celestial equator. This arbitrary sphere 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 further south the observer is located. The southern counterpart is the southern celestial hemisphere.

Astronomy

In the context of astronomical discussions or writing about celestial cartography, the northern celestial hemisphere may be referred to as the Northern Hemisphere.

For celestial mapping, astronomers may conceive the sky like the inside of a sphere divided into two halves by the celestial equator. The Northern Sky or Northern Hemisphere is therefore the half of the celestial sphere that is north of the celestial equator. Even if this geocentric model is the ideal projection of the terrestrial equator onto the imaginary celestial sphere, the northern and southern celestial hemispheres are not to be confused with descriptions of the terrestrial hemispheres of Earth itself.^{[according to whom?]}

Observation

Of the modern 88 constellations, 36 lie predominantly within the northern celestial hemisphere, with 28 completely on the northern hemisphere. The other 8 constellations (Aquila, Canis Minor, Leo, Monoceros, Orion, Pisces, Serpens Caput, and Taurus) lie in some piece on the southern hemisphere.^[1] The northern constellations are:^[2]

The North Star, the brightest star in the constellation Ursa Minor, has been used extensively throughout history to find north due to its brightness and proximity to north celestial pole.