Parallax:
The apparent change in position of a star caused by the annual motion of the
earth.
Perigee:
The point in the orbit of the moon or artificial satellite nearest the earth.
Perihelion:
The point on an orbit nearest the sun.
Planet:
Large spherical object shining by a star. Our planets are: Mercury, Venus,
Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto (+Charon ?)
Position angle:
For a binary star, the position angle isthe angle (measured counterclockwise)
at the brighter star between a linedrawn due north to a linedrawn to the
fainter star.
Precession of the equinoxes:
The axis of the earth's rotation slowly changes its direction, maintaining a
constant tilt with respect to the ecliptic and making a complete rotation once
every 26000 years. In consequence, the equinoxes on the intersections of the
celestial equator and the ecliptic slowly drift westward.
Prime vertical:
A great circle on the celestial sphere from the east to the west and passing
through the zenith.
Prominence:
Cloud of gas elevated above the solar surface.
Proper motion:
The apparent drift of a star across the sky, compounded from the motion of the
star and the sun.