zenitális

Zenitális is a term used in astronomy and surveying. It refers to the zenithal point, which is the point directly above an observer on the celestial sphere. Imagine standing on Earth and looking straight up; the point in the sky you are looking at is your zenith. The zenithal direction is perpendicular to the local horizontal plane.

The zenithal distance is the angle between the zenith and a celestial object. It is the complement of the altitude of that object, meaning zenithal distance = 90 degrees - altitude. If an object is at the zenith, its zenithal distance is 0 degrees. As an object gets closer to the horizon, its zenithal distance increases.

The zenithal telescope is a specialized instrument used in astronomical observations, particularly for determining precise positions of stars. These telescopes are designed to observe objects only when they pass through or very near the zenith. This method helps to minimize errors caused by atmospheric refraction, which is less significant at the zenith than at lower altitudes. The concept of the zenith is fundamental in establishing local vertical reference lines in geodesy and surveying.