Free online courseGeneral Astronomy

Course Description

Look up at the night sky and it can feel both familiar and mysterious. This free online course helps you turn that curiosity into real understanding by connecting what you see overhead to the science that explains it. You will learn to think like an astronomer: using models, evidence, and simple physical principles to make sense of motions in the heavens, the changing seasons, and the patterns we recognize as constellations.

The journey starts with how people have interpreted the sky across history and why major shifts in thinking mattered. You will explore the ideas that led from ancient explanations to the Copernican revolution, and how improved ways of reasoning about motion and forces made the universe more predictable and understandable. From there, the course grounds big concepts in everyday experience, showing how perspective, reference frames, and physical laws shape what we observe.

As your skills grow, you will connect Earth-based phenomena to celestial mechanics: why day length changes through the year, how the Moon’s motion produces eclipses, and what makes planetary orbits and sky cycles appear the way they do. You will also take a guided tour of the solar system, learning how planet properties reflect where and how they formed, and how impacts, heat, and internal structure drive the geology of terrestrial worlds.

Atmospheres become another lens for understanding worlds. You will compare the terrestrial planets, see why greenhouse effects differ so dramatically, and learn how atmospheric layers work on Earth along with the role of the magnetic field. The course also links planetary science to our present, examining long-term climate change and how human activity influences atmospheric composition.

Finally, you will move outward to the stars and beyond by learning the language of light. By interpreting spectra, you can infer temperature, composition, and motion, and understand why the Sun shines. You will explore stellar structure, classification, and the Hertzsprung-Russell diagram, then follow how stars are born, evolve, and end their lives—sometimes quietly, sometimes in spectacular supernovae that leave behind white dwarfs, neutron stars, or black holes.

Throughout, quick questions and exercises help you check understanding and build confidence. By the end, you will not only recognize key astronomy ideas, but also be able to explain them clearly—making every clear night an opportunity to read the universe with informed eyes.