Parallax, the difference of direction of a heavenly body as seen from two points, as the centre of the earth and some point of its surface, [69].
Parallels, imaginary circles on the earth or in the heavens parallel to the equator, having the poles for their centre.
Perigee, nearest the earth; said of a point in an orbit.
Perihelion, the point of an orbit nearest the sun.
Periodic time, time of a planet's, comet's, or satellite's revolution.
Personal equation, [65].
Perturbation, the effect of the attractions of the planets or other bodies upon each other, disturbing their regular motion; of Saturn and Jupiter, [11]; of asteroids, [13]; of Uranus and Neptune, [176].
Phases, the portions of the illuminated half of the moon or interior planet, as seen from the earth, called crescent, full, and gibbous.
Photosphere of the sun, [89].
Planet (a wanderer), as seen from space, [99]; speed of, [101]; size of, [102]; movements retrograde and direct, [112].