🌈 Why Rainbows Form
Reflection, refraction, and dispersion of light in water droplets
Rainbows are one of nature's most beautiful optical phenomena, created when sunlight interacts with water droplets in the atmosphere. This interaction involves three key physics principles: reflection, refraction, and dispersion of light.
Reflection in Rainbows
Reflection occurs when light bounces off a surface. In rainbows, sunlight reflects off the inside surface of water droplets.
Why It's Important:
- Creates the characteristic arc shape of rainbows
- Causes light to change direction inside droplets
- Essential for the primary rainbow formation
Limitations:
- Requires precise angle (42° for primary rainbow)
- Some light passes through (not all reflects)
- Dependent on droplet shape and size
Real World Examples:
- Primary Rainbow: Single reflection inside droplets
- Secondary Rainbow: Double reflection (fainter, colors reversed)
- Glory: Backscattering of light creating circular rainbow
Reflection Angle Game
Adjust the angle to create a rainbow (42° for primary, 51° for secondary):
Current Angle: 0°
Refraction in Rainbows
Refraction is the bending of light as it passes from one medium to another (like air to water). This separates white light into different colors.
Why It's Important:
- Bends light into the droplet
- Begins the color separation process
- Determines rainbow's position in sky
Limitations:
- Amount of bending depends on wavelength
- Affected by water temperature and purity
- Can't occur without density change
Real World Examples:
- Prism: Glass refracts light into spectrum
- Oil slicks: Thin film refraction creates colors
- Diamond sparkle: High refractive index bends light dramatically
Refraction Explorer
Select different materials to see how they refract light:
Dispersion in Rainbows
Dispersion is the separation of white light into its constituent colors due to different wavelengths refracting at different angles.
Why It's Important:
- Creates the rainbow color spectrum
- Reveals light's composite nature
- Produces the characteristic color sequence
Limitations:
- Color separation is relatively small in water
- Atmospheric conditions can blur colors
- Some colors overlap (like yellow-green)
Real World Examples:
- CD/DVD: Grooves disperse light into colors
- Camera lenses: Chromatic aberration is unwanted dispersion
- Spectrometers: Use dispersion to analyze light
Create Your Rainbow
Adjust droplet size and sunlight angle to form a rainbow:
Droplet Size: 1.5μm
Sun Angle: 42°
How to See Rainbows
- Position yourself with the sun behind you (early morning/late afternoon best)
- Look for rain or mist in the air opposite the sun
- For the brightest rainbows, find water droplets with uniform size
- Use a garden hose on sunny day to create your own rainbow
- For circular rainbows, view from high altitude (airplane or mountain)
Rainbow FAQs
Why are rainbows curved?
Rainbows are circular because the light is reflected at specific angles (42° for primary) in spherical droplets. We typically see an arc because the ground blocks the lower half.
Can two people see the same rainbow?
No, each person sees their own unique rainbow created by different water droplets. The rainbow you see is specific to your viewing position.
Why is the sky darker between double rainbows?
The area between primary and secondary rainbows (Alexander's band) appears darker because light is being reflected away from this region by the water droplets.
