Answer:
The celestial equator and the ecliptic are two "great circles" on the sky coordinate system.
Think of them as two hoops of the same size, hinged together at two points. If you hold one
steady and spin the other one inside it, they stay connected at the two hinges, but they can
be set at any angle to each other.
Now put them in the sky. Place the steady one right above the equator all the way around, and tilt
the movable one on the hinges so that it makes an angle of 23.5 degrees with the steady one.
The steady one, above the earth's equator all the way around, is the celestial equator. The movable one,
tilted 23.5 degrees to the equator, is the ecliptic ... the path that the sun appears to travel in the sky,
once around in a year. The hinges ... where the ecliptic crosses the equator ... are the points where the
sun is located at the time of the two equinoxes. Halfway between the hinges are the points where the
two circles are farthest apart ... one where the ecliptic is farthest above the equator, the other where
it's farthest below. Those are the points where the sun is located at the time of the two solstices.