| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Physics |
| Lesson Topic: Know that redshift in the light from distant galaxies is evidence that the Universe is expanding and supports the Big Bang Theory |
Learning Objective/s:
- Describe what redshift is and how it is measured in galaxy spectra.
- Explain the relationship between redshift, recession velocity, and Hubble’s Law.
- Interpret how redshift observations provide evidence for an expanding Universe and the Big Bang Theory.
- Calculate approximate recession velocities using v ≈ c z and distances using v = H₀ d.
- Evaluate the significance of the linear redshift‑distance relation as cosmological evidence.
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Materials Needed:
- Projector or interactive whiteboard
- Slide deck with spectra diagrams and Hubble’s Law graph
- Calculator or spreadsheet for quick calculations
- Handout summarising formulas and key concepts
- Spectral line simulation app (optional)
- Whiteboard and markers
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Introduction:
Begin with a striking image of a galaxy spectrum showing shifted lines to capture interest. Ask students what a shift toward longer wavelengths might imply about the galaxy’s motion, linking to prior knowledge of Doppler effects. State that by the end of the lesson they will be able to explain how this observation supports the expanding‑Universe model and the Big Bang Theory.
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Lesson Structure:
- Do‑now (5') – Short written response to “If a galaxy’s spectral lines are shifted to longer wavelengths, what does that indicate about its motion?” (Collect for quick check).
- Mini‑lecture (10') – Define redshift, present the formula z = Δλ/λ₀, and introduce the Doppler approximation v ≈ c z with visual spectra.
- Guided practice (12') – Students calculate recession velocities for given redshifts and then estimate distances using v = H₀ d (H₀ ≈ 70 km s⁻¹ Mpc⁻¹); teacher circulates to support.
- Interactive plotting (10') – Using provided data, groups plot redshift vs. distance, identify the linear trend, and articulate Hubble’s Law.
- Concept discussion (8') – In pairs, students summarise how the redshift‑distance relationship evidences an expanding Universe and connects to the Big Bang narrative; share key points.
- Exit ticket (5') – Write one concise sentence explaining why redshift supports the Big Bang Theory.
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Conclusion:
Recap the chain from observed redshift to recession velocity, Hubble’s Law, and the expanding‑Universe model. Collect the exit tickets to gauge understanding, and assign a brief homework: calculate the distance to a galaxy with z = 0.03 using the formulas practiced today.
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