LOM v1.0networkedLOM v1.02URLhttp://portal.discoverthecosmos.eu/node/159836enThe orbits of the satellites of the major planets change over time due to the gravitational attraction between the satellites and between a given satellite and the body of the planet itself. For example, a satellite raises a tidal "bulge" on the planet, which, in turn, affects the motion of that satellite by expanding or contracting its orbit. This amounts to a very small so-called "tidal" or "secular" acceleration in the satellite's orbital motion that accumulates to become an observable effect over periods of several decades or centuries. Detecting these subtle changes requires not only very accurate satellite astrometry but also regular measurements over very long periods of time. The latter requirement generally precludes the use of spacecraft data for this purpose. Accurate timing and photometry of mutual satellite events, on the other hand, is intrinsically a much better estimator of long-term orbital variation.eclipsesatelliteeclipticoccultationtidal accelerationsecular accelerationplanetsLOM v1.0final1.0LOM v1.0author2009-04-07Vagelis TsamisLOM v1.0publisher2009-04-07Vagelis TsamisenLOM v1.0LOM v1.0creator2009-07-31Sofoklis SotiriouLOM v1.0validator2009-07-31Sofoklis SotiriouLOM v1.0operating systemLOM v1.0ms-windowstext/htmlhttp://portal.discoverthecosmos.eu/node/159836LOM v1.0noLOM v1.0noLOM v1.0activemediumLOM v1.0mediummore than 2 didactic hoursLOM v1.0Guided ResearchLOM v1.0teacherLOM v1.0school education12-15LOM v1.0DisciplineScienceAstronomy: EclipsesAstronomy: OrbitAstronomy: Solar systemAstronomy: PlanetsAstronomy: Satellites