CALIPPUS, author of the CALIPPIC PERIOD. Calippus, of Cyzicus, lived about B.C. 330. He is said to have been a disciple of Plato. He observed at the Hellespont, and is said to have detected the error of the Metonic cycle by means of a lunar eclipse which happened six years before the death of Alexander. Very little more is known of him, and that little not worth stating.
The meaning of the 'Calippic period' may be briefly stated as follows. Suppose a perfectly central eclipse of the moon to a spectator at the earth's centre, that is, suppose the centres of the sun and moon, and the junction of the moon's orbit with the ecliptic, or the node, to be all at the same point of the visible heavens. The revo lutions of these three points, the sun's centre, the moon 'a centre, and the moon's node, would then begin, and a whole cycle of eclipses would take place, in a manner depending. upon the relative motions of the three, until such time as the same phenomenon, namely, the central lunar eclipse, again happened at the same node. After this, the cycle of eclipses would recommence in the same order, because all the cir cumstances of motion on which eclipses depend are recommencing. Thus if the second-hand of a watch were mounted on the same pivot as the minute and hour hand, they would all be together at 12 o'clock, and all the possible phases (appearances) which their relative positions could present would be completed in twelve hours, and then begin again. Next it is evident that though such a coincidence of sun,
moon, and moon's node never take place, the period elapsed between two epochs at which the three are very near to each other will present a succession of eclipses which will nearly be repeated, that is, with nearly the same circumstances, in the next such period.
The oycle of Meton was composed of 235 lunationa, or periods from new moon to new moon, containing a very little more than 255 revo lutions from a node to the same node again, about 254 complete sidereal revolutions of the moon, and 6940 days, or a few hours more than 19 years. This may be called a first approximation, and it is still sufficiently exact for finding Easter.
Calippus observed that a more correct period might be formed by taking four times the period of Meton, all but one day, or 27,759 days, or very nearly 76 years. This period contains 940 oompleto lunations, 1020 nodal revolutions, and 1016 complete sidereal revolutions ; all very nearly. The Calippic cycle is therefore four Metonic cycles, all but one day. The analogy with the common and leap year will fix this in the memory. Calippus began to reckon his cycles from the new moon next following the summer solstice of the year B.c. 330, being the commencement of the third year of the 112th Olympiad, A.U.C. 423, Julian period 4389, era of Nabonassar 418.