If the stars are seen to rise perpendicular to the horizon by an observer, he is located on the:

1. Equator

When an observer located on the Earth`s equator observes the stars, they will appear to rise directly from the eastern horizon and move in a straight path overhead, perpendicular to the horizon. This is because the Earth`s rotation axis aligns with the observer`s position on the equator.

At the equator, the observer is in a position where the celestial equator, an imaginary circle projected into the sky directly above the Earth`s equator, intersects the observer`s horizon. This alignment causes the stars to rise and set vertically, appearing to move directly overhead.

In contrast, observers at different latitudes, such as the Tropic of Cancer, South Pole, or North Pole, would observe the stars rising and setting at different angles relative to the horizon due to the Earth`s tilt and their respective positions on the globe.