As of this writing, the aspens have yet to turn yellow. Make no mistake: The leaves' yellow hue is there, but the trees' chlorophyll production has not diminished sufficiently to reveal it. Why? Many factors can influence the timing of the aspens' changing colors: rainfall, nighttime frost, tree health. You know: It's complicated.

I felt compelled to shake some information out of the internet as it relates to aspens after participating in a series of very silly and, sadly, public debates about when, exactly, the mountain would turn gold—conversations that indicated I had forgotten literally any botanical knowledge I ever possessed. In response to my own idiocy, I spent a happy half hour reading about photosynthesis. Every now and then the internet comes through with something other than ads for leggings and evidence of our crumbling democracy.

And after all, fall isn't just a time for rugging up, joining the leafers and counting the days until Christmas cookies. We're in back-to-school season, and chances are we all have something about which we'd like to learn more. The growth of online education has helped decrease the barriers to doing so. And many learners are taking advantage: According to Class Central, which tracks data related to Massive Open Online Courses (MOOC), the top two providers—Coursera and edX—had, respectively, 37 and 18 million users last year.

Santa Fe Institute is well-known locally for its lectures and programs that deliver its scientists' work to the public, but its online education program attracts users across the world. Complexity Explorer offers a wide variety of courses and mini-tutorials on subjects related to complexity science, many geared toward learners of any level.

SFI's new director for education, Carrie Cowan, recently relocated to Santa Fe from Bay Harbor, Maine, where she was the pre- and postdoctoral education director at biomedical research facility The Jackson Lab. Cowan says Complexity Explorers' users are "self-motivated learners," and that "90 to 95% take the courses for fun."

Upcoming courses include the popular Introduction to Complexity (sign up immediately, the course started Oct. 1), which covers topics such as: dynamics, chaos, fractals, information theory, self-organization, agent-based modeling and networks, and is free of charge. The course has been offered eight times since it launched in 2013 and has been taken by 38,000 students from all over the world.

Other current courses include Introduction to Dynamical Systems and Chaos and, this winter, Fractals and Scaling. If a full-blown course feels unrealistic, Complexity Explorer also offers mini-tutorials on topics such as machine learning, game theory and information theory.

Cowan says one of the goals with Complexity Explorer is to continue developing "more entry points to complexity science" that help integrate real-world examples of how the science is used to make the topics more accessible to the non-complexity-scientists among us. She also hopes to develop a "Choose Your Own Adventure" type of system in which potential enrollees would be guided toward specific courses based on their interests, as well as their levels of expertise and knowledge.

Cowan shifted from research to education after completing her doctorate in molecular cellular biology at University of California, Berkeley. The shift was a result of spending time in the research lab with her students and post-docs and "seeing their pathway through their education." While getting a Ph.D and being able to focus long-term on specific research is valuable, "I think sometimes the good aspects get lost in the stressful aspects, so I felt it was important to make sure that students and postdocs were getting the most value out of their training." More expansively, she says, "I think education is generally how we change the world." (agreed!)

Cowan had been familiar with SFI since graduate school, and sees its online education portal having both an altruistic function—"there is a genuine wish that Complexity Explorer exists" as well as a "tangible benefit in hopefully getting our tools, our discoveries that are made here into the broader world."

Part of that mission includes a volunteer project to translate Complexity Explorer's courses. Since the project began in 2014, volunteers have subtitled the video courses into 63 languages: Arabic, Spanish and Mandarin are the top non-English languages, but volunteers also have subtitled the courses in English for the non-hearing and for those who speak English as as a second language. According to SFI's summer edition of its newsletter Parallax, 467 people have contributed subtitles so far.

"It's so impressive to see how many people have volunteered," Cowan says, "and it really reflects that Complexity Explorer has a real community behind it."

Santa Fe Institute offers both courses and tutorials through its online education portal: complexityexplorer.org/