Student activity · Grades 9–12 · about 15 minutes
Stellar Magnitude Worksheet
Goal: Use the logarithmic magnitude scale to compare how bright stars and other objects look from Earth.
What to do
- Press the “Five magnitudes” preset (Object A magnitude 1, Object B magnitude 6) and record the readouts.
- Press “One magnitude” and record the readouts, then press “Equal brightness”.
- Model Sirius and Polaris: set Object A magnitude to −1.46 (Sirius) and Object B magnitude to 1.98 (Polaris). Record the readouts.
- Swap the values from step 1 (Object A 6, Object B 1) and record the readouts.
Record your results
| Setting | Flux A / Flux B | Brighter object |
|---|---|---|
| Five magnitudes (A 1, B 6) | ||
| One magnitude (A 1, B 2) | ||
| Equal (A 2, B 2) | ||
| Sirius vs Polaris (A −1.46, B 1.98) | ||
| Swapped (A 6, B 1) |
Questions
Which is brighter, a star of magnitude 1 or a star of magnitude 6? By how many times?
How many times brighter is a one-magnitude difference? Show that five such steps make 100.
How many times brighter does Sirius (−1.46) look than Polaris (1.98)?
What happened to the ratio when you swapped the two magnitudes? Explain.
The full Moon has a magnitude of about −12.7, and the faintest stars you can see from a dark site are about magnitude 6. About how many times brighter is the full Moon?
Does a star’s apparent magnitude tell you how much light it actually gives off? Explain.
Free from The Astronomy Lab · theastronomylab.com