APHELION. That point in the orbit of a planet or comet which is most remote from the sun, and at which the angular motion is slowest; being the end of the greater elliptic axis. The opposite of _perihelion_. APHELLAN. The name of the double star α Geminorum, better known as Castor. APHRACTI. Ancient vessels with open waists, resembling the present Torbay-boats. APLANATIC. That refraction which entirely corrects the aberration and colour of the rays of light. APLETS. Nets for the herring-fishery. APLUSTRE. A word applied in ancient vessels both to the ornament on the prow and to the streamer or ensign on the stern. Here, as in the rudder-head of Dutch vessels frequently, the dog-vane was carried to denote the direction of the wind. APOBATHRÆ. Ancient gang-boards from the ship to the quays. APOCATASTASIS. The time in which a planet returns to the same point of the zodiac whence it departed. APOGEE. That point of the moon's orbit which is furthest from the earth; the opposite of _perigee_. The _apogee_ of the sun is synonymous with the _aphelion_ of the earth. The word is also used as a general term to express the greatest distance of any heavenly body from the earth. A-POISE. Said of a vessel properly trimmed. APOSTLES. The knight-heads or bollard timbers, where hawsers or heavy ropes are belayed. APOTOME. The difference of two incommensurable mathematical quantities. APPALTO. The commercial term for a monopoly in Mediterranean ports. APPARATUS. Ammunition and equipage for war. APPAREL. In marine insurance, means the _furniture_ or appurtenances of a ship, as masts, yards, sails, ground gear, guns, &c. More comprehensive than _apparatus_. APPARELLED. Fully equipped for service. APPARENT. In appearance, as visible to the eye, or evident to the mind, which in the case of astronomical motions, distances, altitudes, and magnitudes, will be found to differ materially from their real state, and require correcting to find the true place. APPARENT EQUINOX. The position of the equinox as affected by nutation. APPARENT HORIZON. _See_ HORIZON. APPARENT MOTION. The motion of celestial bodies as viewed from the earth. APPARENT NOON. The instant that the sun's centre is on the meridian of a place. APPARENT OBLIQUITY. The obliquity of the ecliptic affected with nutation. APPARENT PLACE OF A STAR. This is the position for any day which it seems to occupy in the heavens, as affected with aberration and nutation. APPARENT TIME. The time resulting from an observation of the sun--an expression _per contractionem_ for apparent solar time. APPARITION. A star or planet becoming visible after occultation. _Perpetual apparition_ of the lesser northern circles, wherein the stars being above the horizon, never set. APPEARANCE. The first making of a land-fall: formerly astronomically used for phenomenon and phase. The day of an officer's first joining a ship after his being appointed.