An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

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.

→ impact; → parameter