pitch angle

In the case of a spiral galaxy, the pitch angle is the angle between a tangent to a spiral arm in a spiral galaxy and the perpendicular to the direction of the galactic center; it gives a measure of how tightly the spiral arms of a galaxy are wound.


In the case of charged particle moving in a magnetic field, the pitch angle is the angle between the direction of a magnetic field and a particle's spiral trajectory in this field. In a non-uniform magnetic field, it changes as the ratio between the perpendicular and parallel components of the particle velocity changes. In the case of the geomagnetic field, pitch angle is important because it is a key factor in determining whether a charged particle will be lost to Earth's atmosphere or not.