Understanding Rainbows

Introduction

• Lecture on rainbows, featuring discussion with Jack Netland, high school physics teacher.
• Focus on why rainbows are curved, inspired by a question from Mrs. W.A. Lynn of Gibbon, Nebraska.

Basic Concept

• Rainbows are seen through rain or tiny glass beads (as in the demonstration).
• Jack uses a model of a raindrop to explain the phenomenon.
• Light refraction and dispersion inside raindrops create a spectrum of colors.

Process of Rainbow Formation

• **Light Refraction: **
  • Sunlight enters one side of a raindrop and bends.
  • Light bounces off the back of the raindrop and exits, bending again.
  • This process creates a spectrum of colors.
  • A specific angle of 42 degrees is formed between incoming and refracted light.

Visibility of Rainbows

• Rainbows are visible when sunlight is low, usually during morning or evening.
• The sun must be behind the observer, and raindrops should be in front.
• Although rainbows are everywhere during rainstorms, they are only visible from certain positions.
• Each observer sees their own unique rainbow based on their perspective.

Why Rainbows are Curved

• Explanation using a model:
  • Light enters at a specific angle (42 degrees) relative to the observer.
  • As the observer moves, the perspective changes, tracing out a circular arc.
• Result: Rainbows appear curved due to the sweeping motion of light at constant angle.
• In some situations, a complete circular rainbow can be observed, especially from an elevated position like an airplane.

Double Rainbows

• Primary and Secondary Rainbows:
  • Primary rainbow: Formed by one internal reflection (42-degree angle).
  • Secondary rainbow: Formed by two internal reflections (51-degree angle).
• Secondary rainbows appear outside the primary rainbow and have inverted color orders.

Conclusion

• The curvature of rainbows is due to geometric optics and the viewer's perspective.
• The idea of a pot of gold at a rainbow’s end is mythical as the rainbow moves with the observer's perspective.

Fun Fact

• The mythical pot of gold is unattainable since the rainbow moves as the observer tries to reach it.

Closing

• Jack Netland provides a colorful and enriching explanation of the phenomenon.