There are currently over 700 known exoplanets, however the Kepler space craft has reportedly found another 1000, although many have not yet been confirmed by ground based observations. Jupiter sized Exoplanets are reasonably easy to detect, but Earth sized ones are extremely difficult, but Kepler may now have found some.
In collaboration with the University of Portsmouth we are helping final year students find stars that have Exoplanets and measure the change in their magnitudes as the stars are transited by one of their planets. Generally the dip in magnitude is a very small percentage of the stars brightness. Although Kepler, in space, can measure dips of just fractions of a percentage that is almost impossible from Earth due to our varying weather conditions and atmospheric effects.
After recording very many eclipses it is possible to determine the period of rotation of the planet about its star and indeed identify if its period is reducing - as it appears to be in several cases as some Exoplanets are orbiting very close to their parent star.
The students gain experience of using the telescopes and CCD cameras and teasing out the results obtained over several weeks of observing.