evection

(i-vek -shŏn) The periodic (31.807 day) inequality in the motion of the Moon that may amount to a displacement in longitude of up to 1°16′20″.4. It arises from changes in the eccentricity of the Moon's orbit (0.0432 to 0.0666) that are brought about by solar attraction. Evection was discovered by the Greek astronomer Hipparchus. See also annual equation; equation of center; parallactic inequality; variation.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006

evection

[ē′vek·shən]

(astrophysics)

A perturbation of the moon in its orbit due to the attraction of the sun.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Evection

the greatest disparity—that is, deviation from motion according to Kepler’s laws—in the moon’s motion around the earth, caused by perturbation by the sun. Discovered by Hip-parchus in the second century B.C., evection was detected by Ptolemy in the second century A.D. and was correctly explained by I. Newton. The change in the moon’s longitude owing to evection reaches 1°16’26” and varies with a period of approximately 31.8 mean solar days. The perturbing force that causes evection also changes the horizontal parallax of the moon periodically.

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References in periodicals archive

* Half-period of the lunar evection (15 days, 21 hours, 45 min = 22905 min).

These are the solar day (1440 min), the stellar day (1436 min), the calendar year (525 600 min), the stellar year (525 969 min), the lunar day (1490 min), the lunar month (registered as the "near-27-day period"), and the period of the lunar evection (45 809 min).

General relativity theory explains the Shnoll effect and makes possible forecasting earthquakes and weather cataclysms

So, the known manifestations of the evection in the near-Earth space motivated the studies of its contribution to the results of [delta][phi] assessments obtained during observations of the total solar eclipses, from 1919 till 1973.

The evection values were calculated upon the Julian dates of the total solar eclipses.

2 shows the distribution of dependency of optical results from the evection. Continuous curve, which includes 0.93" (1919) and 2.73" (1936) values, represents averaging of results depending on the evection and is described as:

The dotted curve, which excludes 0.93" (1919) and 2.73" (1936) values, represents averaging of results depending on the evection and is described as follows:

2, deflection of beams in the evection extremes ([+ or -] 1.274[degrees]) should correspond to [delta][phi] [approximately equal to] 2.25 [+ or -] 10%, and to [delta][phi] [approximately equal to] " 1.72 in case of 0, i.e., conform to the Einstein result.

The role of evection in optical measurements of light beam deflection from the sun's disk (the Einstein effect)

Analysing regularities in the change of the histogram shape, we found periods corresponding to the periodical deviations of the Moon from the Keplerian orbit: variation (14.8 days) and evection (31.8 days).

3.1 The shape of histograms changes with the periods of evection and variation

We compared series of both 1-min and 1-h histograms in the regions of the putative periods: 762[+ or -]6 h (a 31-day period, evection), 648[+ or -]6 h (a 27-day period) and 355[+ or -]6 h (a 15-day period, variation).

However, the period that corresponds to evection is, ceteris paribus, much more pronounced.

3 shows the results of this analysis, which was made in the region of evection period.

Changes in the shape of histograms constructed from the results of [sup.239]Pu alpha-activity measurements correlate with the deviations of the moon from the Keplerian orbit