Lesson Plan

• State the current best estimate of the Hubble constant in s⁻¹ and km s⁻¹ Mpc⁻¹.
• Explain the relationship v = H₀ d and use it to estimate cosmic distances.
• Convert H₀ between s⁻¹ and km s⁻¹ Mpc⁻¹ units.
• Compare at least two observational methods for measuring H₀ and discuss the Hubble tension.
• Apply H₀ to calculate the distance to a galaxy from its recession velocity.

• Projector or interactive whiteboard
• Slide deck with equations, unit conversions, and diagram
• Handout containing H₀ conversion table and sample data
• Calculators or spreadsheet software
• Worksheet with galaxy recession‑velocity problems
• Short video clip on the Hubble tension (optional)

Begin with a striking image of distant galaxies and ask, “How could we know how far they are just by looking at their light?” Connect this to students’ prior knowledge of red‑shift from earlier astronomy lessons. Explain that today they will discover the key constant that links red‑shift to distance and how scientists arrive at its current value.

1. Do‑now (5 min): Quick written question – “If a galaxy’s light is shifted to longer wavelengths, what does that tell us about its motion?” Collect responses.
2. Mini‑lecture (10 min): Introduce H₀, present v = H₀ d, show unit conversion (s⁻¹ ↔ km s⁻¹ Mpc⁻¹) and the current value 2.2 × 10⁻¹⁸ s⁻¹ (≈ 68 km s⁻¹ Mpc⁻¹).
3. Interactive demonstration (8 min): Use an online graph to plot recession velocity versus distance; students observe the slope representing H₀.
4. Group activity (12 min): In pairs, calculate distances for a set of given velocities using H₀ and record results on the worksheet.
5. Method comparison discussion (10 min): Review standard candles, CMB fitting, and gravitational‑wave “standard sirens”; highlight differences and the Hubble tension.
6. Exit ticket (5 min): Write one sentence summarising why knowing H₀ is crucial for estimating the age of the Universe.

Recap the definition of H₀, its numerical value, and how it links velocity to distance. Emphasise the ongoing debate among measurement techniques and its impact on cosmology. For homework, assign a short problem set requiring conversion between units and distance calculations for additional galaxy data.