Rainbows appear low in the sky because of the angle at which sunlight is refracted and reflected inside raindrops. This angle, approximately 42 degrees, dictates the rainbow's position relative to the observer and the sun.
Understanding Rainbow Formation
Here's a breakdown of how rainbows form and why their height varies:
- Sunlight and Raindrops: Rainbows occur when sunlight shines on raindrops.
- Refraction: As sunlight enters a raindrop, it slows down and bends (refracts) because water is denser than air.
- Reflection: The light then reflects off the back of the raindrop.
- Refraction (Again): As the light exits the raindrop, it refracts again.
- The 42-Degree Angle: The angle between the incoming sunlight and the outgoing light after the two refractions and one reflection is approximately 42 degrees. This specific angle is critical for the rainbow's visibility.
Why Rainbows Appear at Different Heights
The rainbow's height depends on the position of the sun in the sky:
- Low Sun, High Rainbow: When the sun is low in the sky (near sunrise or sunset), the center of the rainbow appears higher, and you see more of its arc. Because the center of the bow must be opposite the sun, a low sun means a high center, giving the rainbow a greater vertical extent.
- High Sun, Low Rainbow: When the sun is high in the sky, the center of the rainbow is lower, potentially even below the horizon. In this case, you might only see a small portion of the rainbow, or none at all. This is because the 42-degree angle means the rainbow is formed below your line of sight.
- Observer's Position: Rainbows are also observer-dependent. Different observers will see slightly different rainbows because their perspective relative to the sun and raindrops is unique.
In essence, low rainbows are visible when the sun is higher in the sky, while higher rainbows are visible when the sun is lower. The consistent factor is the 42-degree angle at which the light is bent and reflected within the raindrops.
