What is the term for the point on the celestial sphere that is directly above the observer?

The term for the point on the celestial sphere that is directly above the observer is the zenith. This point represents the highest position relative to an observer's local horizon, effectively serving as a reference for celestial measurements and observations. The zenith is an important concept in fields such as astronomy and surveying, as it is used to define vertical angles and to understand the position of celestial objects as they relate to an observer's viewpoint.

The horizon is the line where the earth's surface and the sky appear to meet, while the nadir refers to the point directly opposite the zenith, located below the observer, indicating the lowest position on the celestial sphere relative to that observer. The ecliptic is the apparent path of the Sun across the celestial sphere over the course of a year, which is not related to the specific point directly above the observer. Understanding these terms provides a solid foundation for interpreting celestial navigation and related surveying concepts.