1 Values used in computing an occultation of a star or planet by the Moon. They include the Universal Time (UT) of conjunction in right ascension between the Moon and the star (or planet); the Greenwich hour angle of the star (or planet) at that time; and values of particular geometrical properties of the Moon, the star (or planet), and the observer's location.
2 Eight values used in computing the circumstances of a solar eclipse. They describe the position and direction of the axis of the Moon's shadow, and the size of the shadow relative to the Earth. Besselian elements are named after F. W. Bessel, who devised the method of computation.