At what latitude of the Earth can you see: a) all the stars of the celestial hemisphere at any moment of the night;

At what latitude of the Earth can you see:
a) all the stars of the celestial hemisphere at any moment of the night;
b) stars of only one hemisphere (northern or southern);
c) all the stars of the celestial sphere?

a) At any latitude, at any moment half of the celestial sphere is visible;
b) at the poles of the Earth, the northern and southern hemispheres are visible, respectively;
c) all the stars of the celestial sphere can be seen at the equator of the Earth in less than a year.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.