Online Courses
Courses are suitable for people who prefer structured learning about a specific topic, but keep in mind they take time and commitment to complete. This is only a small sampling of the kinds of free courses you can find online. Search on Coursera, or EdX for a more exhaustive list.
Note: Coursera courses are free but certificates must be paid for. Specializations (a collection of related courses) are not free.
The Science of the Solar System– Caltech
Journey of the Universe- A Story for Our Times (specialization)- Yale University
Origins- Formation of the Universe, Solar System, Earth and Life– University of Copenhagen
Introduction to Thermodynamics: Transferring Energy from Here to There– University of Michigan
From the Big Bang to Dark Energy– University of Tokyo
Astronomy: Exploring Time and Space– University of Arizona
Mechanics: Motion, Forces, Energy and Gravity, from Particles to Planets– The University of New South Wales
MIT OCW is another great, classic resource. They have courses on everything from physics to history.
STEM From Scratch 