Ap"sis (#), n.; pl. Apsides (#). See Apse. [L. apsis, absis, Gr. , , a tying, fastening, the hoop of a wheel, the wheel, a bow, arch, vault, fr. to fasten.]

1. Astron.

One of the two points of an orbit, as of a planet or satellite, which are at the greatest and least distance from the central body, corresponding to the aphelion and perihelion of a planet, or to the apogee and perigee of the moon. The more distant is called the higher apsis; the other, the lower apsis; and the line joining them, the line of apsides.

2. Math.

In a curve referred to polar coordinates, any point for which the radius vector is a maximum or minimum.

3. Arch.

Same as Apse.


© Webster 1913.

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