How big is the open-source community?

There are many variations of this question. For example, "How many unique individuals have ever pushed code upstream successfully?", or "How many active open-source projects currently exist", or "How many individuals have pushed code upstream in the past year to any well-known project."

I'm particularly interested in estimating the number of active projects, and the number of active developers across all projects, where "active" is less well-defined, but perhaps reflects activity within the past year.