Original Title:

Photometry of the Mutual Events
(Eclipses & Occultations)
Between the Jovian Satellites

Keywords:

eclipse satellite ecliptic occultation tidal acceleration secular acceleration planets

Description:

The 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.