Sun dogs, also known as parhelia, are atmospheric optical phenomena that appear as bright spots of light on either side of the sun, often forming a halo around it. They are caused by the refraction, or bending, of sunlight through ice crystals in the atmosphere. Sun dogs typically occur in cold regions or during cold weather conditions.
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Table of Contents
- What are Sun Dogs?
- How do Sun Dogs Work?
- Some Similar Effects
- Discovery of the Spiral Illusion
- References and Resources
What are Sun Dogs?
Sun dogs, also known as parhelia, are atmospheric optical phenomena that appear as bright spots of light on either side of the sun, often forming a halo around it. They are caused by the refraction, or bending, of sunlight through ice crystals in the atmosphere. Sun dogs typically occur in cold regions or during cold weather conditions.
The scientific name for sun dogs is parhelion, which means “beside the sun” in Greek. They are called sun dogs because they often appear as two bright spots of light that follow the sun, similar to faithful dogs following their master.
Sun dogs are usually seen at the same height as the sun, about 22 degrees away from it, and at the same elevation above the horizon. The most common colors observed in sun dogs are red and orange on the side closest to the sun, while the side farther away appears bluish. This coloration occurs because the ice crystals in the atmosphere act as prisms, separating the sunlight into its different colors.
In addition to sun dogs, other atmospheric optical phenomena related to ice crystals include halos, arcs, and sundogs. These can create a variety of beautiful and fascinating light displays in the sky.
How do Sun Dogs Work?
Sun dogs, or parhelia, are created through a combination of refraction and reflection of sunlight by ice crystals in the atmosphere. Here’s a step-by-step explanation of how they form:
- Ice crystals: Sun dogs are typically formed by hexagonal ice crystals present in high-altitude cirrus clouds or in the upper atmosphere. These ice crystals can take on various shapes, such as plates or columns, and are often oriented horizontally as they fall through the atmosphere.
- Sunlight enters: When sunlight passes through these ice crystals, it undergoes refraction, which is the bending of light as it passes from one medium (air) to another (ice crystal). The hexagonal shape of the crystals plays a crucial role in this process.
- Refraction and splitting of light: As sunlight enters an ice crystal, it refracts or bends, separating into different colors (wavelengths) due to the prism-like effect of the crystal. This is similar to how light passes through a glass prism and creates a rainbow spectrum.
- Deflection and focusing: The bent light waves inside the ice crystal then bounce off the interior surfaces, or facets, of the crystal. This process deflects the light and causes it to exit the crystal at specific angles.
- Formation of sun dogs: The deflected light waves exit the ice crystals at angles of approximately 22 degrees. This is where the sun dogs appear relative to the sun. The deflected light can create bright spots of light on either side of the sun, often accompanied by a halo or a circular ring around the sun.
- Coloration: The separation of sunlight into its different colors during refraction can give rise to the characteristic coloration of sun dogs. The side of the sun dog closest to the sun often appears reddish or orange, while the side farther away may have a bluish tinge.
The combination of sunlight passing through ice crystals, refraction, deflection, and the specific angles of exit result in the formation of sun dogs as beautiful optical phenomena in the sky.
Some Similar Effects
There are several atmospheric optical phenomena that are similar in terms of their formation and appearance. Here are a few examples:
- Halos: Halos are circular or ring-shaped displays of light that surround the sun or the moon. They are caused by the refraction and reflection of sunlight or moonlight by ice crystals in the atmosphere. Halos can appear as a complete circle or partial arcs and often have a whitish or color spectrum appearance.
- Circumzenithal Arc: The circumzenithal arc is a rainbow-like arc that appears in the sky, usually located above the sun. It is formed by the refraction of sunlight through ice crystals, similar to sun dogs and halos. The arc is typically bright and displays a vibrant range of colors.
- Sun pillars: Sun pillars are vertical shafts of light that appear above or below the sun. They are caused by the reflection of sunlight by ice crystals in the atmosphere, usually in cold or icy conditions. Sun pillars can give the impression of a tall column of light extending upward or downward from the sun.
- Cloud iridescence: Cloud iridescence is a phenomenon where parts of a cloud display vivid and shimmering colors. It occurs when sunlight is diffracted or scattered by water droplets or ice crystals within the cloud, causing the colors to spread out and create a beautiful iridescent effect.
These are just a few examples of atmospheric optical phenomena that share similarities with sun dogs. Each phenomenon is caused by the interaction of sunlight with atmospheric particles, such as ice crystals or water droplets, resulting in stunning displays of light and color in the sky.
Discovery of the Sun Dogs
While the exact origin of the discovery of sun dogs is difficult to pinpoint, these atmospheric phenomena have been observed and studied by scientists and sky enthusiasts for centuries. Here are a few notable individuals who have contributed to the understanding and study of sun dogs:
- Aristotle: The ancient Greek philosopher Aristotle, who lived from 384 to 322 BCE, made observations and wrote about various atmospheric phenomena, including halos and parhelia. His work laid the foundation for early understanding of these optical effects.
- Christiaan Huygens: A Dutch mathematician, physicist, and astronomer, Christiaan Huygens (1629-1695) made significant contributions to the study of light and optics. He conducted experiments and wrote extensively on the nature of light and its behavior, including the formation of halos and other atmospheric phenomena.
- Anders Jonas Ångström: A Swedish physicist and astronomer, Ångström (1814-1874) made significant contributions to the field of spectroscopy. He studied the diffraction of light by ice crystals and contributed to the understanding of how the size and shape of ice crystals influence the appearance of sun dogs.
- William Henry Pickering: An American astronomer, Pickering (1858-1938) conducted extensive research on atmospheric optics, including sun dogs. He observed and documented various atmospheric phenomena, contributing to the scientific understanding of their formation and characteristics.
- Les Cowley: Les Cowley is a contemporary British atmospheric optics enthusiast and founder of the website Atmospheric Optics. His website is a valuable resource for understanding and exploring various atmospheric optical phenomena, including sun dogs. Cowley has extensively documented and photographed these phenomena, sharing his knowledge and passion with others.
References and Resources
In addition to the Sun Dogs, check out our complete list of illusions and this awesome similar illusions: Platform 9 3-4, Moving Diamond, Moving Ball, Scintillating Stars, Circle Spiral, Moving Hearts, Expanding Flower, Moon Illusion, Face Mosaic
We hope you enjoyed these Sun Dogs!