Your first journey through astronomy

Travel from a changing Moon to the history of the universe. Each stop introduces a new scale or way of reasoning, using a question rather than a list of facts. The main explanations need no prior astronomy; activities and mathematics are optional.

Plan your journey

Allow roughly an hour for the main reading across eight stops, or spread it across several sessions. Investigations can extend the journey substantially. Bookmark any stop to return later. There is no required completion sequence or stored score.

Follow the questions

1. Why does the Moon change shape?

   Predict the Moon's appearance by following its sunlit half around Earth.

   Visual reasoning
2. How big is our Solar System?

   Build a proportional model that separates planet size from the distances between planets.

   Ratios
3. What can starlight tell us?

   Use a spectrum to reason about temperature, elements, and motion.

   Reading a labeled graph
4. Why are some stars bright but cool?

   Use temperature, radius, and luminosity to understand the H–R diagram.

   Ratios and graphs
5. What happens when stars grow old?

   Trace conditional stellar pathways to white dwarfs, neutron stars, and black holes.

   No prior astronomy
6. Black Holes: Start Here

   Build an evidence-led picture of horizons, falling matter, and open questions.

   No prior astronomy
7. What holds a galaxy together?

   Compare orbital observations with an explicit mass model and ask what dark matter means.

   Simple graphs
8. How do we know the universe was hotter and denser?

   Bring together expansion, the microwave background, and primordial elements.

   No prior astronomy

Follow a question a little further

Keep the eight stops as a short route through astronomy, and branch out when a question catches your attention. The Moon leads to eclipses; stars lead to distance and parallax; galaxies lead to our view from inside the Milky Way. Before the final stop, cosmic expansion supplies the geometry behind a changing universe. These are optional branches, not extra requirements for finishing the journey.

Connect the evidence

At the final stop, compare the Moon’s phase pattern with the microwave background. Both help us infer a physical situation, but they involve different observations, models, and scales. Explain why “we cannot visit it” does not mean “we cannot test explanations about it.”

You can check your explanation against the worked examples and limitations on the linked pages. To choose another path, return to Journeys.