Free online courseIntroduction to Astronomy - Solar System, Stars and Cosmology

Course Description

Introduction to Astronomy - Solar System, Stars and Cosmology is a free online course from OpenStax that builds a clear, science-based understanding of the universe, from what we see in the night sky to the deepest questions of cosmology. It starts with the foundations of scientific thinking in astronomy, including scales and measurement, numbers, and how light and time shape our view of distant objects.

You will develop practical sky-knowledge through core concepts such as the celestial sphere, coordinate systems, seasons, calendars, lunar phases, tides, and eclipses, while also exploring how astronomy grew from ancient observations to modern methods. The course then strengthens your grasp of orbital motion and the physical laws that govern planetary and satellite trajectories.

A major focus is learning how astronomers extract information from light. You will cover electromagnetic radiation, spectra, atomic structure and spectral lines, and the Doppler effect, then connect those ideas to the tools used in real observations, including optical, radio, and space telescopes and modern detectors.

From there, the course surveys the Solar System in depth: planet types, formation and dating of solar system objects, Earths interior and atmosphere, climate change and impacts, the Moon and its origin, terrestrial planets, giant planets and their moons, rings, dwarf planets, asteroids, comets, meteors, the Kuiper Belt, and the discovery of exoplanets.

It continues outward into stellar astronomy and astrophysics, covering the Sun, solar activity and space weather, stellar brightness and spectra, the H R diagram, distance methods like parallax and standard candles, the interstellar medium, star formation, and the full arc of stellar evolution through supernovae, neutron stars, and compact binaries. You will also engage with relativity, black holes, and gravitational waves, then move to galaxies, dark matter, large-scale structure, the expanding universe, the Big Bang, and dark energy. The journey concludes with astrobiology and the scientific search for life beyond Earth.