Final answer:
The point where the Earth and sky appear to meet is called the horizon, a key concept in understanding the celestial sphere and the movement of celestial objects across the sky.
Step-by-step explanation:
The point where the Earth and sky seem to meet is known as the horizon. When one observes the sky, whether during the day or at night, the horizon is that circular boundary that creates the illusion of a dome of sky above us. This effect is more perceivable in open spaces such as the sea or flat prairies. The horizon is an integral concept in understanding the celestial sphere, which is a model that astronomers use to describe the apparent motion of the stars and other celestial objects.
The top of the dome, which is the point directly above an observer's head, is termed the zenith. On a clear night, away from city lights, the celestial sphere gives the appearance of a hollow dome with the observer at the center. Ancient astronomers and cultures, who regularly gazed upon the stars, watched them rise on the eastern horizon, move across the dome, and set on the western horizon, fostering the impression of Earth being at the center of a great celestial sphere.