Where on the earth would you have to be for the celestial equator to be perpendicular (make a 90 degree angle) to your horizon?

You would have to be in either the North or South pole.

Explanation:

The stars serve as a guide to realize if you are - or not - in the equator. Since the stars don't set or rise in the horizon, rather earth's movement creates this illusion, you would have to be in the North or South pole for you to see the celestial equator in a 90-degree angle to the horizo