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Line 1: ~~{{More references\|date=April 2011}}~~ In [[astronomy]], '''secular phenomena''' are contrasted with phenomena observed to repeat periodically. In particular, astronomical [[ephemeris\|ephemerides]] use ''secular'' to label the longest-lasting or non-oscillatory perturbations in the motion of planets, as opposed to ''periodic'' perturbations which exhibit repetition over the course of a time frame of interest. [[Solar system]] ephemerides are essential for the navigation of [[spacecraft]] and for all kinds of space observations of the [[planets]], their [[natural satellite]]s, [[star]]s and [[galaxies]].

Secular phenomena: Difference between revisions