IGCSE Physics: Stellar Classification & HR Diagram | Edexcel Modular | Unit 9 | L4

This lesson covers spec points 9.7, 9.8, 9.11P and 9.12P (9.11P and 9.12P Physics only) of the Edexcel
Modular IGCSE Physics specification — classifying stars by colour and surface temperature, representing
brightness using absolute magnitude, and drawing and using the Hertzsprung–Russell (HR) diagram.

PowerPoint includes:
• Retrieval starter reviewing stellar evolution from L3
• Direct Instruction (I Do) — star colour linked to surface temperature; absolute magnitude introduced as
brightness at a standard distance; the HR diagram built up axis by axis (temperature decreasing left to
right, luminosity/absolute magnitude increasing up); the major regions identified — main sequence,
giants, supergiants and white dwarfs
• Guided Practice (We Do) — three guided tasks plotting and classifying stars on the HR diagram, with
answers revealed
• Check for Understanding — 3 MCQs on colour–temperature, the HR axes and stellar regions; answers on
following slides
• Independent Practice (You Do) — activity sheet with exam-style questions
• Review and Reflect — exit ticket on classifying a given star

Activity Sheet includes:
• Exam-style questions progressing from linking colour to temperature, to placing stars on the HR diagram
and identifying the main regions
• A stretch question explaining why a hot star can still be dim (white dwarf)
• Full mark scheme for teacher use

Note: spec points 9.11P and 9.12P are Physics-only content (marked throughout).