Some rainbows appear "flat" because of the sun's position in the sky; the higher the sun, the flatter the rainbow.
Understanding Rainbow Formation and Shape
Rainbows are optical phenomena caused by refraction, internal reflection, and dispersion of light in water droplets, resulting in a spectrum of light appearing in the sky. While we often imagine them as perfect semi-circles, their appearance can vary significantly.
Factors Influencing Rainbow Appearance:
| Factor | Influence on Rainbow Shape |
|---|---|
| Sun's Height | The height of the rainbow's arch is inversely related to the sun's altitude. |
| Observer's Position | The observer must be between the sun and the water droplets. |
| Water Droplets | Rainbows are created in the presence of rain droplets. |
The Sun's Angle and Rainbow Height
The key reason for "flat" rainbows lies in the sun's angle relative to the horizon. A rainbow's arch extends downwards from the horizon, with its center point opposite the sun.
- High Sun: When the sun is high in the sky, the rainbow's center point is also high above the horizon. This results in a smaller portion of the rainbow's arc being visible, creating the appearance of a "flat" or low rainbow. Rainbows cannot occur when the sun is above 42°, meaning that the flattest rainbows happen when the sun is relatively high. You'll rarely see a full, classic rainbow around lunchtime because of the sun's position (09-Jul-2024).
- Low Sun: Conversely, when the sun is low (near sunrise or sunset), the rainbow's center point is low, and more of the arc is visible. This allows us to see a higher, more complete rainbow.
Examples:
- Morning/Evening Rainbows: These are typically more arched because the sun is closer to the horizon.
- Midday Rainbows: These are "flatter" because the sun is higher in the sky. You might only see a small arc.
Therefore, a "flat" rainbow isn't incomplete but rather reveals only a portion of its full arc due to the sun's angle.
