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Science

Stars, Galaxies, and the Universe

Overview

Students zoom out from the solar system to explore the structure of the universe, discovering the almost incomprehensible scale of stars, galaxies, and the cosmos.

Learning Objective
Students understand the scale of the universe from stars to galaxies to the observable universe, and can describe the life cycle of a star.

Resources needed

  • None

Lesson stages

0 / 7 done
  1. 1 Recap: our solar system has one star — the Sun. But how many stars are there in the universe?
  2. 2 Introduce: our galaxy, the Milky Way, contains approximately 200 to 400 billion stars.
  3. 3 There are estimated to be over 2 trillion galaxies in the observable universe.
  4. 4 Introduce light-years: the distance light travels in one year — about 9.5 trillion km. The nearest star is 4.2 light-years away.
  5. 5 Describe the life cycle of a star: nebula to main sequence star (nuclear fusion of hydrogen) to red giant to white dwarf for Sun-like stars; OR supernova to neutron star or black hole for massive stars.
  6. 6 Ask: where do heavy elements like iron, gold, and uranium come from? (Supernova explosions).
  7. 7 Ask: how do we know about distant galaxies we cannot reach? (Light — all our knowledge of the universe comes from electromagnetic radiation).

Tap a step to mark it as done.

Variations

  • Compare the size of different types of stars — the Sun is mid-sized; some stars are a thousand times larger.
  • Discuss the Big Bang theory and the evidence for it (cosmic microwave background, redshift of galaxies).
  • Explore what a black hole is and why light cannot escape from one.
More information

Teach: star, galaxy, light-year, nebula, fusion, supernova, black hole, universe. The scale of the universe is genuinely incomprehensible — use analogies and ratios to make it manageable.

Focus on the life cycle of a star and the concept of light-years before introducing galaxy counts and the scale of the universe.

Can students describe the life cycle of a star like the Sun? Can they explain what a light-year is and why we use it?

No resources needed. Draw the stellar life cycle as a flowchart in soil.

Students often think the Sun is an average or small star. The Sun is actually slightly larger than average — most stars are smaller, cooler red dwarf stars.

Cosmology and stellar physics connect physics to the largest scales of existence. Understanding that all the atoms in our bodies were forged in stars is one of science's most profound insights.

Activity details
Secondary Medium 25 minutes no prep Whole Class, Small Group Indoor & Outdoor
Topics
Stars Galaxies Universe