Abstract

Since 1995 the study of planets around stars other than the sun has been one of the most exciting and fastest-growing fields in astrophysics. We now know of about 300 such exoplanets. The subset of exoplanets which happen to have their orbits aligned so they pass directly between us and the host star, i.e. those which “transit” their host star are particularly interesting. Only for these transiting exoplanets can we measure the radius, and thus deduce the density of the planet. Furthermore, the transits offer the opportunity to make direct detections of atomic and molecular species in the exoplanet atmosphere via transmission spectroscopy. We can also measure otherwise inaccessible properties of the host star, such as the alignment of its spin. Finally, we can detect the tiny drop in the infrared flux when the planet passes behind the star. I will introduce this field, and show some of the recent observational results, placing them in the context of the models for exoplanet structure and evolution.