Beta angle

In orbital spaceflight, the beta angle (${\displaystyle {\boldsymbol {\beta }}}$) is the angle between a satellite's orbital plane around Earth and the geocentric position of the Sun. The beta angle determines the percentage of time that a satellite in low Earth orbit (LEO) spends in direct sunlight, absorbing solar energy.

The beta angle does not define a unique orbital plane: all satellites in orbit with a given beta angle at a given orbital altitude have the same exposure to the Sun, even though they may be orbiting in different planes around Earth.

The beta angle varies between +90° and −90°, and the direction in which the satellite orbits its primary body determines whether the beta angle sign is positive or negative. An imaginary observer standing on the Sun defines a beta angle as positive if the satellite in question orbits in a counterclockwise direction and negative if it revolves clockwise. The maximum amount of time that a satellite in a normal LEO mission can spend in Earth's shadow occurs at a beta angle of 0°. A satellite in such an orbit spends at least 59% of its orbital period in sunlight.