Finally only three telescopes saw the occultation from the North of Chile, that is to say TRAPPIST (see article Astronomers from Liège in seventh heaven) at La Silla and two small telescopes at San Pedro de Atacama. For the other telescopes, the telescope-TNO-star alignment was not perfect and the occultation did not take place. It should be explained that you must be in exactly the right spot because a very precise coincidence of 5 millionths of a degree between the position of Eris and the occulted star was required, which represents the angle at which a one Euro coin is observed from a distance of 150 km!

This type of observation requires availability of the telescope at any time and a capacity to react very quickly. “I was contacted the day before the phenomenon”, explains Emmanuël Jehin, scientific co-manager of the TRAPPIST telescope. “I was told: We think from the latest predictions that it will be perfect for you in Chile. Can you carry out the experiment tomorrow? At the time, I was observing the comet Hartley 2 with the Very Large (VLT) European Telescope from the observatory of Paranal, also located in Chile. I took the controls of TRAPPIST remotely, made the necessary calibrations and I was ready to observe the occultation at the appointed time. Not all the big observatories have such flexibility. TRAPPIST itself was designed to provide this level of availability! I began the observations half an hour before the event and two minutes from the predicted time I was suddenly able to see the star disappear for thirty seconds. Eris was blocking the light from the star! It was an observation that astronomers had dreamt of carrying out for years! Since then, TRAPPIST has become an important element in this observation network, and other successes on large TNOs have been recorded and will be published soon.”