Institute for Advanced Study / Princeton University Joint Astrophysics Colloquium

The iconic spiral arms that decorate the disks of massive galaxies (like our own Milky Way) have been studied observationally and theoretically since they were first recorded 180 years ago, nevertheless the exact details of their nature remains elusive. I will review what is known observationally about spiral arms, including results from the citizen science project Galaxy Zoo (www.galaxyzoo.org) and the large galaxy survey “MaNGA” (Mapping Nearby Galaxies at Apache Point Observatory - part of the SDSS). I will discuss how these and other observational data are being used to constrain the variety of different physical models which have been proposed to explain spiral arms in galaxies.