What phenomenon explains why one pole is always above the horizon?

The phenomenon that explains why one pole is always above the horizon is the rotation of the Earth. As the Earth rotates on its axis, it creates the cycle of day and night. Because of this rotation, observers at specific latitudes will always have one pole (the North or South Pole) remaining above their horizon at certain locations.

For instance, if you are located at the North Pole, the entire southern hemisphere will always be below your horizon, and from your vantage point, you cannot see the South Pole. Conversely, at points near the equator, the poles will be on the horizon at certain times but will never be permanently above it. This rotation is a fundamental aspect of Earth's behavior that explains the constant visibility of one of the poles depending on your geographic location.

The other options like precession and revolution around the sun relate to different astronomical phenomena. Precession affects the orientation of Earth's axis over thousands of years, revolution influences seasonal changes, and orbital eccentricity deals with the shape of Earth's orbit, none of which directly explain why one pole remains above the horizon for an observer at a stable point on Earth's surface.