(astronomy) The point of a body's elliptical orbit about the system's centre of mass where the distance between the body and the centre of mass is at its minimum. In the case of other celestial bodies, specialised terms are used. See Apsis (Wikipedia) for details.
The most appreciable changes in their orbits occur approximately every 6.2 years, when the periapsis of Pandora lines up with the apoapsis of Prometheus and the moons approach to within about 1,400 kilometres (870 mi).
The anomalistic period is the time that elapses between two passages of an object at its periapsis (in the case of the planets in the Solar System, called the perihelion), the point of its closest approach to the attracting body.
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In all cases, the direction of A lies along the symmetry axis of the conic section and points from the center of force toward the periapsis, the point of closest approach.
From Venus orbit insertion to July 1980, periapsis was held between 142 and 253 kilometres (88 and 157 mi) (at 17 degrees north latitude) to facilitate radar and ionospheric measurements.