A solar halo is a luminous ring or arc around the sun, caused by the refraction and reflection of sunlight by ice crystals suspended in the Earth's atmosphere. The reference defines it as a "luminous halo parallel to the horizon at the altitude of the sun; caused by ice crystals in the atmosphere."
Understanding Solar Halos
Here's a more detailed look at what solar halos are and how they form:
Definition and Synonyms
According to the reference material:
- A solar halo is defined as a luminous halo parallel to the horizon at the altitude of the sun; caused by ice crystals in the atmosphere.
- Synonyms for solar halo include:
- Parhelic circle
- Parhelic ring
Formation
Solar halos are optical phenomena that occur due to:
- Ice Crystals: The primary ingredient is the presence of tiny ice crystals, typically hexagonal in shape, suspended in high-altitude cirrus or cirrostratus clouds.
- Refraction and Reflection: As sunlight passes through these ice crystals, it is refracted (bent) and reflected. The specific angles at which the light bends (typically 22° or 46°) create distinct rings or arcs around the sun.
Common Types of Solar Halos
- 22° Halo: This is the most common type of solar halo, appearing as a bright ring with a radius of approximately 22 degrees around the sun. It’s created as light passes through the 60° angle of hexagonal ice crystals.
- Parhelia (Sun Dogs): These are bright spots or patches of light that appear on either side of the sun, often located along the 22° halo.
- Circumhorizontal Arc: A rare and vividly colored arc that appears parallel to the horizon, below the sun.
Why Study Solar Halos?
While beautiful to observe, understanding solar halos provides insights into atmospheric conditions:
- Weather Forecasting: The presence of cirrus clouds, which cause halos, can indicate an approaching weather system.
- Atmospheric Composition: Studying halos helps us understand the composition and behavior of ice crystals in the upper atmosphere.
Practical Insights
- Safety First: Never look directly at the sun, even when observing a solar halo. Use a suitable filter or indirect viewing methods.
- Photography: Use a wide-angle lens to capture the entire halo.
In summary, a solar halo is an impressive atmospheric phenomenon born from the interaction of sunlight and ice crystals, offering both visual delight and scientific value.
