What is the effect of the precession of the celestial sphere?
The precession of the Earth causes an apparent precession of the celestial sphere resulting in the movement or processional translation of the celestial poles. That is to say, the celestial poles move around the constellations in a circular fashion or the north celestial pole tends to move away from Polaris. Hence Polaris is not permanent pole star.
What are the North Polar Region and the South Polar Region, with reference to constellations?
The northern hemisphere of the celestial sphere is called the North Polar Region. The converse is true for the South Polar Region.
What is the absolute and apparent visible brightness of a celestial body?
The Sun is visually brighter than the Moon and the Moon is visually brighter than the stars when viewed in the sky. However, the brightness is only the apparent brightness since some of the stars have actually greater absolute brightness than the Sun and seem less bright only because they are very much further away than the Sun.
If it were possible to keep all the celestial bodies at the same distance from Earth and view them, then we would get to know their real or absolute brightness relative to one another.
Absolute brightness can be ascertained only through calculations unlike apparent value from visual observations.