URBANA (AP) — Talk about a big class: One professor at the University of Illinois started the fall semester with nearly 32,000 students from around the world.

Professor Jonathan Tomkin is teaching "Introduction to Sustainability" through the online learning platform Coursera. The Urbana-Champaign campus is offering seven free online classes this fall, joining Princeton, Stanford, the University of Michigan and other schools that have already partnered with Coursera to offer online classes.

Sending an email to tens of thousands of students can be nerve-wracking, said Tomkin, who teaches in the School of Earth, Society and Environment.