  In terms of scientific output, the best way to study solar system bodies is
sending spacecraft to make in-situ measurements or to observe at close
distance. Probably, the second best means to learn about important physical
properties of solar system objects is through stellar occultations. By
combining occultation observations from several sites, size and shape can be
derived with kilometric accuracy. Also, atmospheric properties can be derived
if the body has an atmosphere. Furthermore, the technique can detect rings and
even satellites (although rarely) around the main body. Except for the very
special cases of Pluto and Charon, stellar occultations by Transneptunian
Objects (TNOs) had never been observed until October 2009. This was because the
ephemeris of the TNOs have much larger uncertainties than their angular
diameters (typically of the order of ~10 milliarcsecond) and also because
stellar catalogs were not accurate to the milliarcsecond level. Despite the
difficulties, at the time of this writing, 43 occultations by 22 different
Trans-Neptunian Objects, and 17 occultations by 5 Centaurs have been detected
thanks to the efforts of several teams. Due to the complications of accurately
predicting and observing these events, most of the successes have been achieved
through wide international collaboration, which is a key issue to succeed in
observing stellar occultations by TNOs. Multichord occultations are typically
detected at a rate of ~3 per year on average, whereas the majority of the
observed occultations are single-chord detections, which means that only one
site detects the occultation. In these cases, no tight constraints on size and
shape can be derived from those observations alone. Here we review most of the
aspects involved in the complex process to successfully observe occultations,
and present some of the lessons learned.
