Wait what? We still haven’t figured out how to measure the size of a galaxy? Come for fika and I’ll tell you a story about how the development of imaging in astronomy, from the use of photographic plates in the 1930s to current CCD imaging, impacted the definition and measurement of galaxy size. You’ll get to view some of the oldest and newest deep images of galaxies and learn about a new physically motivated galaxy size definition that challenges our current understanding of how galaxies evolve. Excitingly, the new definition of size can be adopted in upcoming deep, wide imaging surveys such as Rubin Observatory’s LSST. So get ready folks, this stuff might show up in large scale catalogues of the future and then you’ll be able to tell others where it came from!