The celestial sphere is
used to make it easier to find objects in space.
Since the Earth is round,
picture the celestial sphere as a hollow glass circle with the Earth
floating in the center. All the stars we see are glued onto
the inside of the glass circle. This makes it simple to attach
coordinates to the sphere and find stars or planets.
The north and south
celestial poles are located directly above Earth's north and south
poles. Since the north celestial pole is located directly
above true north, its altitude is the same as the observer's
latitude on Earth.
The celestial equator is
Earth's equator projected straight out into the sphere
Earth is tilted at a 23
degree angle. So the ecliptic is at a different 23 degree
angle on the sphere. It crosses the celestial equator at 2
points. These points are called equinoxes. The Sun moves
along the ecliptic and passes the 2 equinoxes on March 21 (the
Vernal equinox) and September 21 (the autumnal equinox).