A rainbow-like ring around the sun is called a halo. It is caused by the refraction of sunlight through ice crystals present in thin, high-altitude cirrus clouds.
Understanding Solar Halos
A solar halo isn't a true rainbow caused by raindrops. Instead, it's an optical phenomenon that happens when sunlight bends as it passes through the hexagonal ice crystals in cirrus clouds. These crystals act like tiny prisms, each refracting and dispersing the sunlight. This results in a ring of light, which often appears white but can sometimes show color, with red on the inside and violet on the outside – similar to how a rainbow is formed.
How Halos Form:
- Ice Crystals: High-altitude cirrus clouds are composed of millions of tiny ice crystals, which have a specific hexagonal shape.
- Light Refraction: When sunlight passes through these ice crystals, it is refracted or bent. Because the crystals are prism-shaped, the light is not only bent but also dispersed into different colors.
- Ring Appearance: The bending and dispersion of light by many crystals at a specific angle (usually around 22 degrees) creates a circle of light, visible as a halo around the sun.
- Coloration: While usually white, if the refraction is more pronounced, you may see the colors of the rainbow with red being on the inner part and violet on the outer part.
Key Characteristics of Solar Halos:
| Feature | Description |
|---|---|
| Shape | Circular ring around the sun |
| Color | Usually white but can sometimes have a rainbow-like effect (red inner, violet outer) |
| Cause | Refraction of sunlight through ice crystals in cirrus clouds |
| Visibility | Best seen when the sun is behind a thin veil of cirrus clouds. |
Practical Insights
- Not a Sign of Bad Weather: While often thought to indicate a change in weather, halos can occur at any time and are often unrelated to storms. They simply indicate the presence of ice crystals in high clouds.
- Safety Reminder: Never look directly at the sun, even when observing a halo. Doing so can cause serious eye damage. Use specialized filters or indirect methods to observe solar halos safely.
- Photography: If you are taking pictures of a halo, use a wide-angle lens to capture it in its entirety. You can experiment with different exposure settings to get the best photo.
In conclusion, the rainbow ring around the sun is a halo, resulting from light refracting through ice crystals in high cirrus clouds. These halos are beautiful optical phenomena that display the interaction between light and atmospheric conditions.
