from The American Heritage® Dictionary of the English Language, 4th Edition
- n. Solar perturbation of the lunar orbit.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. Modification of the lunar orbit due to the gravitational effects of the Sun.
from the GNU version of the Collaborative International Dictionary of English
- The act of carrying up or away; exaltation.
- An inequality of the moon's motion in its orbit, due to the attraction of the sun, by which the equation of the center is diminished at the syzygies, and increased at the quadratures by about 1° 20'.
- The libration of the moon.
from The Century Dictionary and Cyclopedia
- n. The act of carrying out or away; a lifting up; exaltation.
- n. In astronomy: The second lunar inequality, described by Ptolemy.
- n. The moon's libration.
This he called the evection, and introduced another epicycle to represent it.
In quadrature, however, where the half-moon formed a right angle at the earth with the sun, the distance moon-earth had to be reduced to conform with this “evection,” as it was called later.
His chief discovery was an irregularity of the lunar motion, called the '_evection_.'
He was a working astronomer, and he made at least one original discovery of some significance -- namely, the observation of a hitherto unrecorded irregularity of the moon's motion, which came to be spoken of as the moon's evection.
Moreover, such observations as the precession of the equinoxes and the moon's evection are as yet unexplained, and measurements of the earth's size, and of the sun's size and distance, are so crude and imperfect as to be in one case only an approximation, and in the other an absurdly inadequate suggestion.
(The equation of the centre, discovered by Hipparchus.) (_a_) The evection, discovered by Hipparchus and Ptolemy.
It then gives Ptolemy's own great discovery -- that which has made his name immortal -- the discovery of the moon's evection or second inequality, reducing it to the epicyclic theory.
Praefect the superintendence of the Cursus Publicus, that excellent institution by which facilities for intercourse were provided between the capital and the most distant Provinces, relays of post-horses being kept at every town, available for use by those who bore properly signed 'letters of evection.'
Praefect remained responsible for the supply of their food; and the charge of the _Cursus Publicus_ was accordingly retransferred -- at any rate in the Eastern Empire -- to the office of the Praefect, though the letters of evection still required the counter-signature of the
(_a_) The first true perturbation is what Ptolemy called "the evection," the principal part of which is a periodic change in the ellipticity or excentricity of the moon's orbit, owing to the pull of the sun.
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