The Shape of a Rainbow

A rainbow is one of nature's most spectacular optical phenomena. While we commonly see it as a colorful arc in the sky, its true shape holds some fascinating surprises.

The Complete Circle

1. A rainbow is actually a complete circle, not just an arc.
2. From the ground, we typically only see the upper half because:
   • The horizon blocks the lower portion
   • The viewing angle requires the sun to be behind us
   • Water droplets need to be at a specific angle (42 degrees) from our line of sight

Special Viewing Conditions

1. Full circular rainbows can be seen in special circumstances:
   • From an airplane
   • While spraying water on a sunny day
   • Near waterfalls on a sunny day
   • Through artificial mist or fountain displays

The Science Behind the Shape

The circular shape of a rainbow occurs because:

• Sunlight enters water droplets in the air
• The light is reflected and refracted
• Different wavelengths (colors) exit at slightly different angles
• The critical angle for this phenomenon is approximately 42 degrees

Double Rainbows

Sometimes you might see a double rainbow, where:

• The primary bow shows the usual color order (red on top)
• The secondary bow appears above with reversed colors
• The area between them appears darker (Alexander's dark band)

Factors Affecting Visibility

The visibility and appearance of a rainbow depend on:

1. Sun position (must be behind the viewer)
2. Time of day (best seen in early morning or late afternoon)
3. Weather conditions (needs sunlight and water droplets)
4. Viewing angle (observer must be at the right position)

Interesting Facts

• Every person sees their own unique rainbow
• The higher the sun, the lower the rainbow appears
• No two people see exactly the same rainbow
• Rainbows can never be reached as they move when you move

Rainbow Viewing Tips

To best observe a rainbow:

1. Position yourself with your back to the sun
2. Look for them after rain when the sun comes out
3. Early morning or late afternoon provides the best viewing times
4. Higher elevations can offer better viewing angles

Understanding the true circular nature of rainbows helps us appreciate this natural phenomenon even more, even though we usually only see half of its majestic form from our earthbound perspective.