Parallax in Altitude. Difference between altitude of heavenly body above sensible horizon and its altitude above rational horizon. Is maximum when body is in sensible horizon.
Parallel Index. Lines parallel to the bearing-marker on a radar display, useful for passing an intended distance from a point of land or vessel.
Parallel of Altitude. Small circle parallel to plane of horizon and passing through all points having the same altitude.
Parallel of Declination. Small circle of celestial sphere that passes through all points having the same declination.
