Starlight

Brightness and colour

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Hotter stars are bluer, cooler stars are redder.
• Wien's law: $\lambda_\text{peak} = 2.9 \times 10^{-3}/T$. The Sun peaks around 500 nm.
• Apparent brightness falls as 1/d².

Steps

1. Red and blue stars
2. Colour and temperature
3. Sun’s peak
4. Magnitudes
5. Two magnitudes
6. Dimmer with distance