Additionally the observed altitudes are cleared of dip and semidiameter.

Since the shadow's edge represents the limb of the sun, he must correct the value for the semidiameter of the sun.

A module (Latin modulus, a measure) is a term that was in use among Roman architects, corresponding to the semidiameter of the column at its base.

In the case of the Moon, additional corrections are needed for the Moon's horizontal parallax and its apparent semidiameter; both vary with the Earth-Moon distance.

In geometry, the semidiameter or semi-diameter of a set of points may be one half of its diameter; or, sometimes, one half of its extent along a particular direction.

In sunrise/sunset tables, the assumed semidiameter (apparent radius) of the Sun is 16 minutes of arc and the atmospheric refraction is assumed to be 34 minutes of arc.