Curtation is a derived term of curtate.

In astronomy|lang=en terms the difference between curtation and curtate

is that curtation is (astronomy) the interval of a planets orbit in which its curtate or shortened distance is less than the true distance while curtate is (astronomy) said of the distance of a planet from the sun or earth, as measured in the plane of the ecliptic, or the distance from the sun or earth to that point where a perpendicular, let fall from the planet upon the plane of the ecliptic, meets the ecliptic.

As a noun curtation

is (astronomy) the interval of a planets orbit in which its curtate or shortened distance is less than the true distance.

As an adjective curtate is

shortened, having been shortened.