Free online course Introduction to Astronomy - Solar System, Stars and Cosmology

About the free online course

Look up at the night sky and it can feel both familiar and impossible to grasp. This course turns that sense of wonder into understanding by giving you the scientific tools astronomers use to explain what we see, from the daily motion of the stars to the evolution of the universe itself. You will learn how astronomy became a modern science, how evidence separates reliable explanations from speculation, and how scale and time change the way we think about distance, motion, and cosmic history.

You will also gain confidence in navigating the sky. By working with celestial coordinates and the geometry of the celestial sphere, you will be able to describe where objects are and why they appear to move. The same clear approach connects to seasons, calendars, phases of the Moon, tides, and eclipses, helping you understand why these cycles repeat the way they do and why they sometimes do not line up as our intuition expects.

A major thread of the course is learning how we know what we know. Light becomes your primary messenger: you will see how electromagnetic radiation carries information, why different kinds of spectra matter, and how Doppler shifts reveal motion across enormous distances. You will understand how telescopes and detectors extend human vision, why observatories operate across the entire spectrum, and what space-based instruments can do that ground-based ones cannot.

From there, the course builds a coherent picture of the solar system and beyond. You will connect planetary types, formation ideas, impacts, atmospheres, moons, rings, comets, asteroids, and the methods used to detect planets around other stars. As the focus shifts outward, stars come into view as physical objects with measurable properties, life cycles, and endpoints that create neutron stars, black holes, and supernova explosions.

Finally, you will bring it all together at galactic and cosmological scales, exploring the structure of the Milky Way, galaxy types, active galaxies, dark matter, dark energy, and the evidence behind the Big Bang model. Throughout, quick checks and practice questions reinforce the reasoning process so you finish with a grounded, big-picture understanding of astronomy that you can apply to news, observations, and lifelong curiosity.