Ellinogermaniki Agogi Observatory

CCD Imaging and Photometry of the Mutual Events of Saturnian Satellites
Observational Campaign PHESAT-09 – IMCCE

Scientific Background
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.

The Mutual Events
In 2008-2010, a series of eclipses and occultations will occur among the satellites of Jupiter and Saturn thanks to the equinox on these planets occurring in 2009. The observation of these events provides valuable data to the astronomical scientific community.

IMCCE
The Institut de Mecanique Celeste et de Calcul des Ephemerides (IMCCE, formerly Bureau des Longitudes) has been organising observing campaigns of these events since 1973 with the objective of providing the long time series necessary to isolate these tidal effects and use them as proxies for the interior of these bodies, effectively doing geophysics through ground-based photometry.

EA Observatory
Ellinogermaniki Agogi Observatory is taking part in this international campaign, contributing valuable scientific data to the astronomical community. Using a 40cm SCT, an Atik 16HR CCD camera and a standard Bessell I (infrared) filter, we have already successfully observed 2 such events involving satellites of Saturn, in 19/12/08 and 24/12/08. We hope to observe several more in January and July of 2009 together with numerous events among the Galilean satellites of Jupiter throughout the summer and autumn period.
These results will be eventually published in the professional astronomy literature.

Sofoklis Sotiriou (Ellinogermaniki Agogi, GR)
Vagelis Tsamis (Hellenic Astronomical Association, GR)
Apostolos Christou (Armagh Observatory, UK)