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ANOMALY (from Gr. lwvw)

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Originally appearing in Volume V02, Page 80 of the 1911 Encyclopedia Britannica.
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ANOMALY (from Gr. lwvw) .iaXta, unevenness, derived from dv- privative, and i aXos, even), a deviation from the See also:common See also:rule. In See also:astronomy the word denotes the angular distance of a See also:body from the pericentre of the See also:orbit in which it is moving. Let AB be the See also:major See also:axis of the orbit, B the pericentre, F the See also:focus or centre of See also:motion, P the position of the body. The anomaly is then the See also:angle BFP which the See also:radius vector makes with the major axis. This is the actual or true anomaly. Mean R anomaly is the anomaly which the body would have if it moved from the pericentre around F with a See also:uniform angular motion such that its revolution would be completed in its actual See also:time (see ORBIT). See also:Eccentric anomaly is defined thus: Draw the circumscribing circle of the elliptic orbit around the centre C of the orbit. Drop the perpendicular RPQ through P, the position of the See also:planet, upon the major axis. Join CR; the angle CRQ is then the eccentric anomaly, In the See also:ancient astronomy the anomaly was taken as the angular distance of the planet from the point of the farthest recession from the See also:earth. See also:Kepler's Problem, namely, that of finding the co-ordinates of a planet at a given time, which is equivalent—given the mean anomaly—to that of determining the true anomaly, was solved approximately by Kepler, and more completely by See also:Wallis, See also:Newton and others. The anomalistic revolution of a planet or other heavenly body is the revolution between two consecutive passages through thepericentre. Starting from the pericentre, it is completed on the return to the pericentre.

If the pericentre is fixed, this is an actual revolution; but if it moves the anomalistic revolution is greater or less than a See also:

complete circumference. An Anomalistic See also:year is the time (365 days, 6 See also:hours, 13 minutes, 48 seconds) in which the earth (and similarly for any other planet) passes from See also:perihelion to perihelion, or from any given value of the anomaly to the same again. Owing to the precession of the equinoxes it is longer than a tropical or sidereal year. by 25 minutes and 2.3 seconds. An Anomalistic See also:month is the time in which the See also:moon passes from See also:perigee to perigee, &c. For the See also:mathematics of Kepler's problem see E. W. See also:Brown, Lunar Theory (See also:Cambridge 1896), or the See also:work of See also:Watson or of Bauschinger on Theoretical Astronomy.

End of Article: ANOMALY (from Gr. lwvw)

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