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This article is about the astronomer and
mathematician. For other uses, see Calippus
Callippus or Calippus (Greek: Κάλλιπος; ca. 370 BC–ca. 300 BC) was
astronomer and mathematician.
Callippus was born at Cyzicus, and studied under Eudoxus of
Cnidus at the Academy of
Plato. He also worked with Aristotle at the Lyceum, which means that he was
active in Athens prior to
Aristotle's death in 322. He observed the movements of the planets
and attempted to use Eudoxus' scheme of connected spheres to
account for their movements. However he found that 27 spheres was
insufficient to account for the planetary movements, and so he
added seven more for a total of 34. According to the description in
Aristotle's Metaphysics (XII.8), he
added two spheres for the Sun, two for the Moon, and one each for
Mercury, Venus, and Mars.
Callippus made careful measurements of the lengths of the
seasons, finding them (starting with the spring equinox) to be 94 days, 92 days, 89 days, and
90 days. This variation in the seasons implies a variation in the
speed of the Sun, called the solar anomaly. He
also followed up on the work done by Meton of Athens to measure the length
of the year and construct an accurate lunisolar calendar. The Metonic cycle has
years and 235 synodic months in 6940 days. The Callippic cycle
synchronizes days per orbit and rotations per orbit within the
Metonic cycle, noting the difference of one after 4 Metonic cycles,
a duration of 76 years. Distinguishing rotations and days infers
knowledge of the precession cycle.
Callippus started his observation cycle on the summer solstice,
330 BC, (28 June in the proleptic Julian calendar).
The cycle's begin position, the stellar position and sidereal hour
timing the eclipse, are used by later astronomers for calibrating
their observations in relation to subsequent eclipses. The
Callippic cycle of 76 years appears to be used in the Antikythera mechanism, an ancient
astronomical mechanical clock and observational aide of the 2nd
century BC (discovered in Mediterranean waters off Greece). The
Mechanism has a dial for the Callippic cycle and the 76 years are
mentioned in the Greek text of the manual of this old device. The
crater Calippus on the Moon is named after him.
- Kieffer, John S. "Callippus." Dictionary of Scientific