Final answer:
The phenomenon described in the question is related to the Earth's position in its orbit around the Sun and the tilt of its axis. It indicates that the observer is at the Earth's poles when the stars rise and set perpendicular to the horizon and when the stars circle the sky parallel to the horizon. When the celestial equator passes through the zenith, it indicates that the observer is at the Earth's equator. And the Sun rising on March 21 and not setting until September 21 is a characteristic of the polar regions during their respective seasons.
Step-by-step explanation:
The phenomenon described in the question is related to the Earth's position in its orbit around the Sun and the tilt of its axis. When the stars rise and set perpendicular to the horizon, and when the stars circle the sky parallel to the horizon, it indicates that the observer is at the Earth's poles. This is because, at the poles, the celestial pole is directly overhead, causing the stars to appear to rotate around it in a circle. The celestial equator passing through the zenith indicates that the observer is at the Earth's equator. And the Sun rising on March 21 and not setting until September 21 is a characteristic of the polar regions during their respective seasons.