Zenith Zenith The zenith is an imaginary point directly "above" a particular location, on the imaginary celestial sphere. "Above" means in the vertical direction opposite to the apparent gravitational force at that location. The opposite direction, i.e. the direction in which gravity pulls, is toward the nadir. The zenith is the "highest" point on the celestial sphere. The word "zenith" derives from an inaccurate reading of the Arabic expression (), meaning "direction of the head" or "path above the head", by Medieval Latin scribes in the Middle Ages (during the 14th century), possibly through Old Spanish. It was reduced to 'samt'
Overhead projector optics that eliminate the "hotspot" in the center of the screen directly above the light source, so that the brightness is uniform everywhere on the projection screen. Critics feel that there are some downsides as these technologies are more prone to failure and have a much steeper learning curve for the user than a standard overhead projector. Overhead projector An overhead projector is a variant of slide projector that is used to display images to an audience. The name is often abbreviated to OHP. An overhead projector works on the same principle as a 35mm slide projector, in which a