Institute for Advanced Study/Princeton University Joint Astrophysics Colloquium

In the Solar system, the planets follow orbits that are aligned with the Sun's equatorial plane to within about 7 degrees. But what about planets around other stars? Many techniques are now available to measure the obliquities of planet-hosting stars, ranging from an effect predicted in the 19th century to several techniques relying on data from the Kepler space telescope. Many exoplanetary systems show good alignment, as in the Solar system. We have also found many planets on highly inclined orbits, and even retrograde orbits. I will explain the observing techniques, present the patterns that have emerged from the data, and discuss the theories that have been proposed to explain these results.