Occultation:  Usually means when a planet or star is hidden by the moon,
    but it also includes “occultation” of a star by a planet or of a
    satellite by a planet or of one planet by another.

Opposition v.  Conjunction.

Parallax:  The error introduced by observing from some point other than
    that required in theory, e.g. in geocentric places because the
    observations are made from the surface of the earth instead of the
    centre, or in heliocentric places because observations are made from
    the earth and not from the sun.

Perigee:  The point in the orbit of a celestial body when it is nearest
    to the earth.

Precession:  Owing to the slow motion of the earth’s pole around the pole
    of the ecliptic, the equator cuts the ecliptic a little earlier
    every year, so that the equinox each year slightly precedes, with
    reference to the stars, that of the previous year.