per·tur·ba·tion

[pur-ter-bey-shuhn]
noun
1.
the act of perturbing.
2.
the state of being perturbed.
3.
mental disquiet, disturbance, or agitation.
4.
a cause of mental disquiet, disturbance, or agitation.
5.
Astronomy. deviation of a celestial body from a regular orbit about its primary, caused by the presence of one or more other bodies that act upon the celestial body.
Origin:
1325–75; < Latin perturbātiōn- (stem of perturbātiō; see perturb, -ation); replacing Middle English perturbacioun < Anglo-French < Latin, as above

Related forms
per·tur·ba·tion·al, adjective
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2013.
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Perturbation is always a great word to know.
So is big bang theory. Does it mean:
a theory that deduces a cataclysmic birth of the universe from the observed expansion of the universe, cosmic background radiation, abundance of the elements, and the laws of physics
the obscuring of the light of the moon by the intervention of the earth between it and the sun, a lunar eclipse, or the obscuring of the light of the sun by the intervention of the moon between it and a point on the earth, a solar eclipse
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Collins
World English Dictionary
perturbation (ˌpɜːtəˈbeɪʃən) [Click for IPA pronunciation guide]
 
—n
1.  the act of perturbing or the state of being perturbed
2.  a cause of disturbance or upset
3.  physics a secondary influence on a system that modifies simple behaviour, such as the effect of the other electrons on one electron in an atom
4.  astronomy a small continuous deviation in the inclination and eccentricity of the orbit of a planet or comet, due to the attraction of neighbouring planets

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Science Dictionary
perturbation   (pûr'tər-bā'shən)  Pronunciation Key 

  1. A small change in a physical system, most often in a physical system at equilibrium that is disturbed from the outside.

  2. Variation in a designated orbit, as of a planet, that results from the influence of one or more external bodies. Gravitational attraction between planets can cause perturbations and cause a planet to deviate from its expected orbit. Perturbations in Neptune's orbit led to the discovery of the object that was causing the perturbation—the planet Pluto. Perturbations in the orbits of stars have led to the discovery of planetary systems outside of our solar system.


The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia Britannica
Encyclopedia

perturbation

in astronomy, deviation in the motion of a celestial object caused either by the gravitational force of a passing object or by a collision with it. For example, predicting the Earth's orbit around the Sun would be rather straightforward were it not for the slight perturbations in its orbital motion caused by the gravitational influence of the other planets. The search for an eighth planet, which culminated in the discovery of Neptune, was undertaken in part because some astronomers believed that the orbit of Uranus was being gravitationally perturbed by some object beyond it.

Learn more about perturbation with a free trial on Britannica.com.

Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
At one stroke, amid much audience perturbation, he unmoored the taboos and let
  them float flamboyantly close to the mainstream.
The entire investment system was in trouble and the mortgage problem was the
  small perturbation which touched off the avalanche.
Our study lends functional support to the idea that perturbation of histone
  methylation promotes cancer.
The paper concludes that a trace perturbation smaller than observational
  uncertainties allows substantially heterodox physics.
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