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Evection

Definitions

  • Webster's Revised Unabridged Dictionary
    • Evection (Astron) 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'.
    • Evection The act of carrying up or away; exaltation.
    • Evection (Astron) The libration of the moon.
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Century Dictionary and Cyclopedia
    • n evection The act of carrying out or away; a lifting up; exaltation.
    • n evection In astronomy: The second lunar inequality, described by Ptolemy. It comes to its maximum value at the quadratures, and disappears at the conjunctions and oppositions. Ptolemy accounted for it by supposing that the apogee of the moon's orbit or deferent of its epicycle recedes to the west at a uniform angular rate of 11°2′ per diem, while the center of the epicycle advances to the east at a uniform angular rate of motion about the earth of 13°11′, the mean sun always bisecting the arc of the zodiac between the lunar apogee and the center of the lunar epicycle. This theory represented the longitudes with remarkable accuracy, but was utterly inconsistent with the most obvious observations respecting the moon's apparent diameter. According to modern astronomy, the evection is a perturbation of the moon by the sun, due to the fact that the sun tends to separate the moon and the earth by attracting more the nearer body. It thus exaggerates the effect of the eccentricity of the moon's orbit when the transverse axis of the latter lies near the line of syzygies.
    • n evection The moon's libration.
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Chambers's Twentieth Century Dictionary
    • n Evection e-vek′shun (astron.) a lunar inequality resulting from the combined effect of the irregularity of the motion of the perigee, and alternate increase and decrease of the eccentricity of the moon's orbit.
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Etymology

Webster's Revised Unabridged Dictionary
L. evectio, a going up, fr. evehere, to carry out; e out, + vehere, to carry: cf. F évection,
Chambers's Twentieth Century Dictionary
L. evection-eme, out, vehĕre, vectum, to carry.

Usage


In science:

Keywords: discriminant, resultant, Morley form, transvectant, evectant, classical invariant theory, Hilbert-Burch theorem.
On the Jacobian ideal of the binary discriminant
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