Science of Rainbows: Why Seven Colors Appear After Rain
After heavy rainfall stops, you might notice a beautiful arc of colors spanning across the sky. This stunning natural phenomenon, known as a rainbow, combines physics principles that create one of nature’s most captivating displays.
Rainbows form through three fundamental physics processes: refraction, reflection, and dispersion of sunlight passing through water droplets suspended in the atmosphere.
How Light Creates Rainbow Colors
Sunlight appears white to our eyes, but it actually contains all colors of the visible spectrum. When sunlight encounters tiny water droplets in the air, these droplets act like natural prisms.
Each individual droplet of water acts as a tiny prism that both disperses the light and reflects it back to your eye. Here’s exactly what happens:
Step 1: Light Enters the Droplet White sunlight enters the water droplet and immediately bends due to refraction. Different wavelengths of light bend at slightly different angles.
Step 2: Color Separation Water droplets in the atmosphere break sunlight into seven colors through dispersion. Red light bends the least, while violet light bends the most.
Step 3: Internal Reflection The rainbow effect occurs because the light is then reflected inside the droplet and finally refracted out again into the air.
Why Rainbow Colors Stay in Order
A sequence of red to violet is produced, because the index of refraction increases steadily with decreasing wavelength. This consistent pattern means rainbows always display colors in the same order:
- Red (outer edge)
- Orange
- Yellow
- Green
- Blue
- Indigo
- Violet (inner edge)
Rainbow’s Perfect Arc Shape
All raindrops refract and reflect the sunlight in the same way, but only the light from some raindrops reaches the observer’s eye. Each raindrop reflects light at approximately 42 degrees, creating the characteristic arc shape.
Ground observers see rainbows as semicircles, but the complete phenomenon actually forms a full circle. Airplane passengers can sometimes observe these complete circular rainbows.
Personal Rainbow Experience
The whole system composed by the Sun’s rays, the observer’s head, and the (spherical) water drops creates a unique viewing experience for each person. Two people standing next to each other will actually see slightly different rainbows because their viewing angles differ.
Perfect Rainbow Conditions
You see a rainbow only when you look away from the sun. Optimal rainbow conditions require:
- Sun behind you
- Rain or water droplets in front of you
- Sunlight breaking through clouds
- Proper viewing angle (42 degrees from antisolar point)
Rainbows demonstrate how simple water droplets can create complex optical phenomena. A rainbow is always formed in a direction opposite to that of the sun, making it a predictable yet magical natural display that showcases the beauty of physics in everyday life.
