APSIS n.
two points of an orbit, as of a planet or satellite, which are at the greatest and least distance from the central body, corresponding to the aphelion and perihelion of a planet, or to the apogee and perigee of the moon. The more distant is called the higher apsis; the other, the lower apsis; and the line joining them…
ASTRONOMY n.
The science which treats of the celestial bodies, of their magnitudes, motions, distances, periods of revolution, eclipses, constitution, physical condition, and of the causes of their various phenomena.
BACKLASH n.
The distance through which one part of connected machinery, as a wheel, piston, or screw, can be moved without moving the connected parts, resulting from looseness in fitting or from wear; also, the jarring or reflex motion caused in badly fitting machinery by irregularities in velocity or a reverse of motion.…