# anomaly

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## anomaly

**1.**

*Astronomy*

**a.**the angle between a planet, the sun, and the previous perihelion of the planet

**b.**the angle between the periapsis of a particular point on a circle round the orbit as seen from the centre of the orbit. This point is obtained by producing a perpendicular to the major axis of the ellipse through the orbiting body until it reaches the circumference of the circle

**c.**the angle between the periapsis of an orbit and the position of an imaginary body orbiting at a constant angular speed and in the same period as the real orbiting body

**2.**

*Geology*

**a.**a deviation from the normal value of gravity at the earth's surface, caused by density differences at depth, for example those caused by a buried mineral body

**b.**a magnetic field, for example one produced by a buried mineral body, that deviates from an expected or standard value, usually that of the earth's magnetic field

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

## anomaly

Any of three related angles by means of which the position, at a particular time, of a body moving in an elliptical orbit can be calculated. For a body S moving around the focus, F, of an orbit (see illustration), the*true anomaly*is the angle

*v*made by the body, the focus, and the point, P, of nearest approach. For a body orbiting the Sun, P is the perihelion. The angle is measured in the direction of motion of S. If an auxiliary circle is drawn centered on the midpoint, C, of the major axis of the elliptical orbit, then the

*eccentric anomaly*is the angle

*E*between CS′ and CP, where S′ lies on the circle and is vertically above S. The

*mean anomaly*is the angle

*M*between P, F, and a hypothetical body moving at a constant angular speed equal to the mean motion of S. It is thus the product of the mean motion and the time interval since S passed P.

The eccentric and mean anomalies are related by *Kepler's equation*:

*E*–

*e*sin

*E*=

*M*

where *e * is the eccentricity of the orbit. The coordinates (*x *, *y*) of the body S can be found from the equations

*x*=

*a*(cos

*E*–

*e*)

*y*=

*a*sin

*E*√(1 –

*e*

^{2})

where *a * is the semimajor axis of the orbit. See also equation of center; orbital elements.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006

## anomaly

[ə′näm·ə·lē] (astronomy)

In celestial mechanics, the angle between the radius vector to an orbiting body from its primary (the focus of the orbital ellipse) and the line of apsides of the orbit, measured in the direction of travel, from the point of closest approach to the primary (perifocus). Also known as true anomaly.

(biology)

An abnormal deviation from the characteristic form of a group.

(geology)

A local deviation from the general geological properties of a region.

(medicine)

Any part of the body that is abnormal in its position, form, or structure.

(meteorology)

The deviation of the value of an element (especially temperature) from its mean value over some specified interval.

(oceanography)

The difference between conditions actually observed at a serial station and those that would have existed had the water all been of a given arbitrary temperature and salinity.

(science and technology)

A deviation beyond normal variations.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

## anomaly

Abnormality or deviation. Pronounced "uh-**nom**-uh-lee," it is a favorite word among computer people when complex systems produce output that is inexplicable. See software conflict and anomaly detection.

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