Solid Angle

A solid angle is a way to measure how large an object appears from a specific point, extending the concept of a regular angle into three dimensions. Think of it as the three-dimensional equivalent of a flat angle, describing how much of the space a viewed object covers around you. It’s measured in steradians (sr). For example, the entire sky around you, if you consider all directions, corresponds to 4π steradians. Solid angles are useful in fields like astronomy, physics, and optics to quantify how much of a sphere an object occupies from a given viewpoint.