The zenith is the point in the sky directly above your head—imagine drawing a straight line from the center of the Earth, through your location, and out into space. This invisible point sits at an altitude of exactly 90 degrees, making it the highest possible point an observer can see in their local sky.</p><p>Every location on Earth has its own unique zenith, which shifts as you move around the globe. When the Sun reaches your zenith, it casts no shadow from a vertical pole—a phenomenon that occurs twice yearly between the Tropics of Cancer and Capricorn (23.5°N and 23.5°S). Ancient Greek astronomers coined the term from the Arabic "samt ar-ra's," meaning "path over the head."</p><p>The zenith serves as a crucial reference point in astronomy and navigation. Sailors historically used sextants to measure star positions relative to the zenith for determining latitude. Modern astronomers prefer observing objects near the zenith because starlight travels through less atmosphere, reducing distortion and providing clearer images. The Hubble Space Telescope, for example, often targets objects when they're closest to zenith from its orbital perspective.</p><p>At any given moment, your zenith point lies exactly opposite to the nadir—the point directly beneath your feet on the opposite side of Earth—creating an invisible vertical line through your position.