An Etymological Dictionary of Astronomy and Astrophysics

1. A measure of the distance by which a collision fails being frontal.
   

2. In → gravitational lensing, the distance of closest approach of the light path to the → lensing object.
   

3. In → rainbows, the displacement of the → incident from an axis that passes through the center of the water droplet.

See also: → impact; → parameter