Linear distance: parsec: : angular diameter:

Angular diameter : degrees or radians

Explanation:

Angular diameter is an angular measurement of the objects. It is an angle subtended by the two points of an object from the observer's eye view.  Its unit is measured in degrees or radians.

It is a geometrical technique used to measure the size of an object which is not directly measurable. For example, to measure the diameter of a planet.

waves moving from a fast medium to a slow medium will experience a reflection as light travels more slowly than red light. total internal reflection occurs when the critical angle is.

truck y has a greater velocity than truck x.