A tiny variation

On the observational level, a star’s vibrations are translated into a periodic variation in its brightness. Nevertheless, the amplitude of this variable luminosity is so minimal that measurements must be precise down to the millionth. The only way to achieve such precision is to collect a maximum of the light emanating from the stars that are to be observed and thus to increase the length of time they are under continuous observation. This objective is difficult to carry out with a telescope fixed on the ground as the data, already polluted by the atmosphere, are cut up into fragments by the day-night cycle and the weather. Alternatively, periods of observation lasting up to 150 days without interruption can be envisaged if a spatial telescope is used.

The CoRoT mission has at its disposal such a telescope, launched from the Baikonur facility on the 27th December, 2006, and placed in orbit at close to 900km above our heads. On the agenda: two exploratory phases of 30 to 60 days each, followed by five central phases of 150 days each alternating with short phases of about 20 days. During the two and a half years that it will function (let’s hope for a longer period) the CoRoT satellite will measure the weak variations in the luminosity of dozens of stars caused by their internal physics and should thus provide access to their hearts.

The variations in brightness to be measured being minimal, it is important not only that the telescope has its back turned permanently to the Sun, but also that its detectors be protected from all light pollution, originating mainly from the Earth. The relative proximity of CoRoT to our planet and the lengthy duration of continuous observation that it will carry out have offered real technological challenges to the satellite's designers. These challenges were nailed down by the Liège Space Center, which developed and perfected the optic baffle which offers the instruments optimal protection.