Coronas

Measuring droplets with a ring

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

• Coronas are diffraction rings from tiny droplets or grains.
• Ring angle $\theta \approx 1.22\lambda/d$: smaller droplets, bigger rings.
• Diffraction puts red outside, the reverse of refraction-based bows.

Steps

1. Rings close to the Moon
2. Measure the droplets
3. Which colour outside?
4. Pollen coronas
5. Corona or halo?
6. Iridescent clouds