Star Color & Luminosity Worksheet
Goal: Explain how a star’s surface temperature sets its color and peak wavelength, and how temperature and size together set its luminosity.
What to do
- Press the “Sun-like” preset. Record the luminosity, peak wavelength and apparent color in the first row of the table.
- Fill in the next three rows by pressing the “Cool dwarf”, “Hot star” and “Sirius A” presets.
- Press “Sun-like” again, keep Star radius at 1 and set Surface temperature to 11,544 K (twice the Sun’s). Record the results.
- Set Surface temperature back to 5,772 K and Star radius to 2. Record the results, then try a radius of 10.
Record your results
| Setting | Luminosity | Peak wavelength | Apparent color |
|---|---|---|---|
| Sun-like (5,772 K, 1 Sun) | |||
| Cool dwarf (3,000 K, 0.2 Suns) | |||
| Hot star (15,000 K, 5 Suns) | |||
| Sirius A (9,940 K, 1.71 Suns) | |||
| Twice as hot (11,544 K, 1 Sun) | |||
| Twice as wide (5,772 K, 2 Suns) |
Questions
Look at your table. As surface temperature goes up, what happens to the peak wavelength and to the star’s color?
When you doubled the temperature and kept the radius the same, by what factor did the luminosity change? Use the formula L/L☉ = (R/R☉)² × (T/5,772 K)⁴ to explain why.
What happened to the luminosity when you doubled the radius? What about at 10 times the radius? Explain.
Predict: a red giant is cooler than the Sun (3,500 K) but 40 times wider. Will it be more or less luminous than the Sun? Then press “Red giant” and record its luminosity.
Sirius A gives off about 26 times as much light as the Sun. Use your table to give two reasons why.
Challenge: a star has a surface temperature of 3,000 K. What radius would it need to be exactly as luminous as the Sun? Calculate it, then check in the lab.
Free from The Astronomy Lab · theastronomylab.com · HS-ESS1-1: Model the Sun’s life span and how energy from fusion in its core reaches Earth as radiation.