Grade 10 · The Universe · Stars and Galaxies
Stars, Galaxies and the Expanding Universe
Follow the evidence — spectra, redshift and cosmic background radiation — that reveals how stars shine and how the universe grew.
Learning objectives
- Explain how nuclear fusion powers stars and produces elements.
- Interpret spectra and redshift as evidence of motion and composition.
- Describe the life cycle of stars of different masses.
- Explain the main lines of evidence for an expanding universe.
NGSS alignment
HS-ESS1-2
Construct an explanation of the Big Bang theory based on astronomical evidence of light spectra, motion of distant galaxies, and composition of matter in the universe.
HS-ESS1-4
Use mathematical or computational representations to predict the motion of orbiting objects in the solar system.
HS-ESS1-6
Apply scientific reasoning and evidence from ancient Earth materials, meteorites, and other planetary surfaces to construct an account of Earth's formation and early history.
HS-ESS2-2
Analyze geoscience data to make the claim that one change to Earth's surface can create feedbacks that cause changes to other Earth systems.
HS-ESS2-4
Use a model to describe how variations in the flow of energy into and out of Earth's systems result in changes in climate.
HS-ESS2-6
Develop a quantitative model to describe the cycling of carbon among the hydrosphere, atmosphere, geosphere, and biosphere.
HS-ESS3-1
Construct an explanation based on evidence for how the availability of natural resources, occurrence of natural hazards, and changes in climate have influenced human activity.
HS-ESS3-3
Create a computational simulation to illustrate the relationships among management of natural resources, the sustainability of human populations, and biodiversity.
HS-ESS3-5
Analyze geoscience data and the results from global climate models to make an evidence-based forecast of the current rate of global or regional climate change and associated future impacts to Earth systems.
MYP criteria
- Criterion A — Knowing and Understanding
- Criterion C — Processing and Evaluating
- Criterion D — Reflecting on the Impacts of Science
ENGAGE
Start here
EXPLAIN
Reading starlight
Stars shine because hydrogen nuclei fuse into helium in their cores, releasing energy as a small amount of mass is converted (E = mc²). Gravity pulling inward balances the outward pressure of radiation, keeping a star stable for millions to billions of years.
Spectra and redshift
Each element absorbs specific wavelengths, producing dark lines in a star's spectrum — a fingerprint of composition. When a galaxy moves away, its lines shift toward longer, redder wavelengths. Distant galaxies show larger redshift, meaning the more distant they are, the faster they recede.
Life cycles and elements
| Star mass | End stage | Elements returned |
|---|---|---|
| Low (Sun-like) | Red giant then white dwarf | Carbon, nitrogen |
| High | Supernova then neutron star or black hole | Oxygen, silicon, iron and heavier |
Three main lines of evidence support an expanding universe from a hot dense beginning: the redshift–distance relation, the cosmic microwave background radiation, and the measured ratio of hydrogen to helium across the cosmos.
Key vocabulary
- Nuclear fusion
- Small nuclei joining to make a bigger one and releasing energy.
- Redshift
- Light from an object moving away is stretched toward the red end.
Practice questions
0/1 correct
Level 4 · Criterion C
Distant galaxies show larger redshift than nearby ones. What does this indicate?
Reflect & track
Your learning log
Saved privately in this browser — no account needed.
How confident do you feel?