PLANETARY

, something that relates to the planets. Thus, we say Planetary worlds, Planetary inhabitants, Planetary motions, &c. Huygens and Fontenelle bring several probable arguments for the reality of Planetary worlds, animals, plants, men, &c.

Planetary System, is the system or assemblage of the Planets, primary and secondary, moving in their | respective orbits, round their common centre the sun. See Solar System.

Planetary Days. With the Ancients, the week was shared among the seven planets, each planet having its day. This we learn from Dion Cassius and Plutarch, Sympos. lib. 4. q. 7. Herodotus adds, that it was the Egyptians who first discovered what god, that is what planet, presides over each day; for that among this people the planets were directors. And hence it is, that in most European languages the days of the week are still denominated from the planets; as Sunday, Monday, &c.

Planetary Dials, are such as have the Planetary hours inscribed on them.

Planetary Hours, are the 12th parts of the artificial day and night. See Planetary Hour.

Planetary Squares, are the squares of the seven numbers from 3 to 9, disposed magically. Cornelius Agrippa, in his book of magic, has given the construction of the seven Planetary squares. And M. Poignard, canon of Brussels, in his treatise on sublime squares, gives new, general, and easy methods, for making the seven Planetary squares, and all others to infinity, by numbers in all sorts of progressions. See Magic square.

Planetary Years, the periods of time in which the several planets make their revolutions round the sun, or earth.—As from the proper revolution of the earth, or the apparent revolution of the sun, the solar year takes its original; so from the proper revolutions of the rest of the planets about the earth, as many sorts of years do arise; viz, the Saturnian year, which is defined by 29 Egyptian years 174 days 58 minutes, equivalent in a round number to 30 solar years. The Jovial year, containing 11 years 317 days 14 hours 59 minutes. The Martial year, containing 1 year 321 days 23 hours 31 minutes. For Venus and Mercury, as their years, when judged of with regard to the earth, are almost equal to the solar year; they are more usually estimated from the sun, the true centre of their motions: in which case the former is equal to 224 days 16 hours 49 minutes; and the latter to 87 days 23 hours 16 minutes.

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Entry taken from A Mathematical and Philosophical Dictionary, by Charles Hutton, 1796.

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PLAFOND
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PLANE
PLANET
PLANETARIUM
* PLANETARY
PLANIMETRY
PLANISPHERE
PLATFORM
PLATO
PLATONIC