The celestial sphere is an imaginary sphere of infinite size surrounding the Earth with the stars embedded in its surface. The Earth blocks half of this celestial sphere from view at any instant. As the Earth rotates different stars come into view. For example, if you are at the Earth's North Pole the bulk of the Earth will always block the Southern Hemisphere's stars from your view. A circle around the celestial sphere which is the extention of the Earth's equatorial plane.
Stars trace out circles around the celestial pole as the Earth rotates.
Stars close to the celestial pole never set because they never come close to the horizon. These are called circumpolar stars . Every day the Sun lies in front of a slightly different location on the celestial sphere due to the Earth's orbital motion. In the course of a year the changing position of the Sun among the stars traces out a complete circle around the sky. This circle is called the ecliptic and represents the apparent path followed by the Sun around the celestial sphere as the Earth orbits the Sun.