Occlusion

is when warm and cold air meet in a DEPRESSION, where the warm air is lifted above the colder air.

Taken from Dictionary of Science

Zenith Distance

the angular distance of a heavenly body from the ZENITH.

Taken from Dictionary of Science

_____________________

The term zenith distance is more often used in astronomy and is the complement of the elevation. That is: 0° in the zenith, 90° on the horizon, up to 180° at the nadir.

Taken from Wikipedia

Oblique Angle

any angle that does not equal 90º (right angle) or any multiple of 90º.

Taken from Dictionary of Science