Latin: a corner, a bend; in this unit.

An angle that has a measure of less than 90°: Tommy's father was visiting at his son's kindergarten and had to sit on one of the little chairs with his legs bent at an an acute angle.

The angle that a ray of sun makes with a line perpendicular to the surface.

A surface that directly faces the sun has a solar angle of incidence of zero, but if the surface is parallel to the sun (for example, sunrise striking a horizontal rooftop), the angle of incidence is 90°.

A natural surface inclination of a slope consisting of loose, well-sorted rock or mineral fragments: An angle of response is the steepest angle of very dry sand, grains, or powder that can form with the level or flat surface without descending down making it look like a natural slope.

The angle between true south and the point on the horizon directly below the sun.

An angle that has a measure of more than 90° and less than 180°.

The angle at which a photovoltaic array is set to face the sun relative to a horizontal position.

The tilt angle can be set or adjusted to maximize seasonal or annual energy collection.

The angle between the direction of interest (of the Sun, for example) and the zenith (directly overhead): The zenith angle is the angle between the direction to the zenith (point of the celestial sphere vertically overhead) and the direction of a light ray.