Pedagogical Callout Showcase
Visual reference for ASTR 201 callout types
Active Learning Callouts
Sample prompt: A star appears to wobble periodically. Which observable is this?
Before reading further, predict: what color will a 10,000 K star appear?
Think: What determines a star’s color? Pair: Compare your answer with a neighbor. Share: One insight from your discussion.
Content Callouts
Physics tells you what relationships are allowed. The inverse-square law isn’t arbitrary—it’s geometry.
Problem: Calculate the frequency of red light (λ = 700 nm).
Solution: \(\nu = c/\lambda = (3 \times 10^{10}\ \text{cm/s}) / (7 \times 10^{-5}\ \text{cm}) = 4.3 \times 10^{14}\ \text{Hz}\)
The inverse-square law follows from geometry: a sphere’s surface area is \(4\pi r^2\). As light spreads over larger spheres, the energy per unit area drops as \(1/r^2\).
Henrietta Leavitt discovered the period-luminosity relation for Cepheids in 1912 while cataloging variable stars in the Magellanic Clouds. She was paid 30 cents per hour.
Structural Callouts
| Section | Topic | Time |
|---|---|---|
| 1.1 | The Four Observables | 10 min |
| 1.2 | The Spoiler Reel | 20 min |
Key points from this section:
- We measure four things directly: flux, position, wavelength, timing
- Everything else is inferred through models
- The gap between measurement and knowledge is where physics lives
Distance measurements aren’t just bookkeeping—they give us the age of the universe. Without Cepheids and supernovae, we wouldn’t know we live in a 13.8-billion-year-old cosmos.
Metacognitive Callouts
“Astronomers measure the temperature of stars directly.”
Wrong. We measure the spectrum (wavelength distribution). Temperature is inferred from Wien’s Law.
A star at 10 pc has apparent magnitude m = 5. What is its absolute magnitude M?
M = m - 5 log(d/10) = 5 - 5 log(1) = 5
Units check: Does \(L = 4\pi r^2 \sigma T^4\) give watts?
\([\text{m}^2][\text{W/m}^2\text{K}^4][\text{K}^4] = [\text{W}]\) ✓
Hubble Tension: Different methods give different values for \(H_0\). Is this measurement error or new physics?