Our physiology is adapted for life in conditions that were very different from the industrial world. A globalized society means increased round-the-clock demand for economic activity, and access to artificial lighting make it possible. Much evidence indicates that disrupted rhythms are linked to disease, thus there is a pressing need to understand our own rhythmic behavior and how it has adjusted to changing social pressures. We are developing techniques to infer rhythms in human activity from patterns in social media use. Our work on rhythms in Twitter use reveal systematic geographical patterns in the timing and duration of rest in different parts of the United States and how these patterns change seasonally.