Microradian

A microradian is a unit of angular measurement, commonly used in fields such as astronomy, optics, and ballistics. It is defined as one millionth of a radian, which is the standard unit of angular measure in the International System of Units (SI). One radian is the angle subtended at the center of a circle by an arc whose length is equal to the radius of the circle. Therefore, one microradian is the angle subtended by an arc of length equal to one millionth of the radius.

The microradian is particularly useful for measuring very small angles, as it allows for precise and accurate calculations in situations where traditional angular units like degrees or minutes of arc would be impractical. For example, in astronomy, the angular resolution of a telescope is often expressed in microradians, as it can be used to determine the smallest detail that can be observed.

In optics, the microradian is used to describe the angular spread of a light beam or the angular resolution of an optical system. In ballistics, it is used to measure the angular deviation of a projectile from its intended target.

The microradian is not an SI unit, but it is recognized by the International Union of Pure and Applied Chemistry (IUPAC) as a coherent derived unit in the SI. It is often abbreviated as μrad, and its symbol is the lowercase Greek letter mu (μ) followed by the lowercase letter "r" (rad).