Lesson Plan

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Lesson Plan
Grade: Date: 17/01/2026
Subject: Physics
Lesson Topic: Know that one light-year is equal to 9.5 × 10^15 m
Learning Objective/s:
  • Describe what a light‑year measures and why it is useful in astronomy.
  • Derive the numerical value of one light‑year using the speed of light and the number of seconds in a Julian year.
  • Convert distances between metres and light‑years, maintaining correct powers of ten.
  • Compare typical astronomical distances using the light‑year unit.
  • Solve a conversion problem involving the distance to Proxima Centauri.
Materials Needed:
  • Projector or interactive whiteboard
  • Calculator (or classroom computers)
  • Worksheet with conversion tables and practice problems
  • Printed handout of typical astronomical distances
  • Scale diagram of the Solar System and Milky Way (poster or slide)
  • Exit‑ticket cards
 Introduction:
Begin with a quick question: “How far would you have to travel to reach the nearest star?” Connect to prior knowledge of the speed of light and the length of a year. Explain that today’s success criteria are to derive the light‑year value, perform conversions, and apply them to real astronomical distances.
Lesson Structure:
  1. Do‑Now (5'): Students write down the speed of light and the number of seconds in a Julian year from memory.
  2. Mini‑lecture (10'): Explain the concept of a light‑year and show the derivation using c × seconds‑in‑a‑year.
  3. Guided Practice (8'): Work through the derivation on the board, checking powers of ten together.
  4. Conversion Activity (12'): In pairs, students use the worksheet to convert given metre distances to light‑years and vice‑versa, referencing the table of typical distances.
  5. Independent Problem (10'): Students solve the Proxima Centauri example and record their answer.
  6. Check for Understanding (5'): Quick quiz on the key points (light‑year definition, formula, conversion factor).
  7. Summary & Exit Ticket (5'): Students write one new fact they learned and a conversion they can perform next time.
Conclusion:
Recap the definition of a light‑year, the derivation steps, and how to convert between metres and light‑years. Collect exit tickets to gauge understanding, and assign homework: research the distance to a chosen star or galaxy and express it in both metres and light‑years.