Nadir is employed during remote sensing of the atmosphere, as well as when an astronaut faces the Earth while performing a spacewalk. The term nadir can also be used to represent the lowest point reached by a celestial body during its apparent orbit around a given point of observation. This can be used to describe the location of the Sun, but it is only technically accurate for one latitude at a time and only possible at the low latitudes. The sun is said to be at the nadir at a location when it is at the zenith at the location's antipode
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