A 22° halo is a circular atmospheric optical phenomenon that forms around the sun or sometimes the moon. It appears as a ring of light at an approximate angle of 22 degrees from the sun or moon.
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Table of Contents
- What are 22° Halos?
- How do 22° Halos work?
- Some Similar Phenomenon
- Discovery of the Spiral Illusion
- References and Resources
What are 22° Halos?
A 22° halo is a circular atmospheric optical phenomenon that forms around the sun or sometimes the moon. It appears as a ring of light at an approximate angle of 22 degrees from the sun or moon. Here are some key features and details about 22° halos:
Formation:
- 22° halos are created by the refraction, reflection, and dispersion of sunlight or moonlight through hexagonal ice crystals in the atmosphere, such as those found in cirrus clouds.
- The hexagonal shape of the ice crystals causes the light to refract at a specific angle of approximately 22 degrees.
- The light rays undergo multiple internal reflections and refractions within the ice crystals, resulting in the formation of a circular halo.
Appearance:
- The halo appears as a complete ring around the sun or moon, with a radius of approximately 22 degrees.
- The halo is usually whitish or colorless, but it may display subtle hints of colors, such as reds, blues, and greens, on rare occasions.
- The inner edge of the halo is typically sharper and more defined than the outer edge.
Position:
- 22° halos are always located at the same angular distance from the sun or moon. They can be seen at an angle of approximately 22 degrees from the center of the sun or moon.
- The halos are typically circular, but their apparent size can vary depending on atmospheric conditions and the observer’s location.
Atmospheric Conditions:
- 22° halos are often associated with the presence of cirrus clouds, which are high-altitude clouds composed of ice crystals.
- These clouds contain ice crystals with the necessary shape and orientation to produce the halo effect.
- The crystals must be aligned in such a way that their flat faces are parallel to the ground.
Similarities with Other Optical Phenomena:
- 22° halos share similarities with other atmospheric optical phenomena, such as sundogs and circumzenithal arcs, which are also formed by the interaction of sunlight with ice crystals.
- These phenomena have different angles of observation and produce distinct shapes and patterns in the sky.
Observation:
- To observe a 22° halo, you need the sun or moon to be relatively low in the sky (usually not at its highest point).
- The halo is best seen when the sky is clear or partly cloudy, allowing for adequate visibility.
22° halos are captivating and beautiful atmospheric phenomena that provide observers with a unique visual experience. Remember to exercise caution and avoid looking directly at the sun to protect your eyes when observing solar halos.
How do 22° Halos Work?
22° halos are formed through a combination of refraction, reflection, and dispersion of sunlight or moonlight as it passes through hexagonal ice crystals in the atmosphere. Here’s a step-by-step explanation of how 22° halos work:
- Sunlight or moonlight: The process begins with sunlight or moonlight. These light sources emit a broad spectrum of colors, ranging from red to violet.
- Hexagonal ice crystals: Cirrus clouds, which are high-altitude clouds composed of ice crystals, play a crucial role in the formation of 22° halos. These clouds contain ice crystals with a hexagonal shape and flat faces.
- Orientation of ice crystals: The hexagonal ice crystals need to be properly oriented with their flat faces parallel to the ground. This specific alignment is crucial for the formation of the halo.
- Incident light: Sunlight or moonlight encounters the ice crystals within the cirrus clouds. The light enters the ice crystal through one face and exits through an adjacent face.
- Refraction: As the light enters the ice crystal, it undergoes refraction, which is the bending of light as it passes from one medium (air) to another (ice crystal). The refraction occurs because the speed of light changes when it enters the denser medium of the ice crystal.
- Internal reflections: Once inside the ice crystal, the light can undergo multiple internal reflections between the crystal faces. These reflections cause the light to bounce around within the crystal.
- Exit refraction: After multiple internal reflections, the light exits the ice crystal through another face. During this exit, the light refracts again, bending as it transitions from the denser medium of the ice crystal back into the less dense medium of the surrounding air.
- Angular dispersion: The refraction of light within the ice crystal causes the different colors (wavelengths) of light to be separated or dispersed. This dispersion occurs because each color of light refracts at a slightly different angle.
- Circular arrangement: The dispersed light from many ice crystals within the cirrus cloud forms a circular pattern around the sun or moon, approximately 22 degrees from its center.
- Halo appearance: The cumulative effect of the refraction, internal reflections, and dispersion results in the formation of a circular halo that appears at an angle of approximately 22 degrees from the sun or moon.
- Coloration: 22° halos are usually whitish or colorless, but they can display subtle hints of colors, such as red, blue, or green. The coloration arises from the dispersion of light within the ice crystals.
The hexagonal ice crystals act as prisms, refracting and reflecting light to create the distinctive circular pattern of a 22° halo. The specific angles and properties of the ice crystals determine the size and appearance of the halo.
Some Similar Phenomenon
There are several atmospheric optical phenomena that are similar to 22° halos in terms of their formation and reliance on ice crystals. Here are a few examples:
- Sundogs (Parhelia): Sundogs are bright spots of light that appear on either side of the sun, usually at a similar altitude. They are caused by sunlight passing through hexagonal ice crystals in the atmosphere and refracting the light to form a halo-like effect.
- Sun pillars: Sun pillars are vertical columns of light that appear above or below the sun. They are created by the reflection of sunlight off flat ice crystals in the atmosphere, resulting in a pillar-like beam of light.
- Circumhorizontal arc (Fire rainbow): This phenomenon appears as a horizontal arc of colors in the sky, typically in a cloudless sky with high-altitude cirrus clouds. It is formed by sunlight passing through horizontally aligned plate-shaped ice crystals in the clouds.
- Tangent arcs: Tangent arcs are faint arcs that appear tangent to the upper or lower portion of a halo, forming a partial circle. They are caused by the interaction of light with specific types of ice crystals in the atmosphere.
- 46° halo: The 46° halo is another circular halo that forms around the sun or moon at an approximate angle of 46 degrees. It is created by the refraction and reflection of light through randomly oriented ice crystals in the atmosphere.
- Lowitz arcs: Lowitz arcs are additional arcs that intersect and extend from the left and right sides of a halo. They are formed by light interacting with complex, plate-like ice crystals in the atmosphere.
- Upper tangent arc: The upper tangent arc is a bright arc that appears tangent to the top of a halo. It is caused by the interaction of light with specific ice crystal orientations.
These phenomena, like 22° halos, are captivating displays of light and color resulting from the interaction of sunlight or moonlight with ice crystals in the atmosphere. They offer unique and stunning visual experiences, adding to the beauty and wonder of the natural world.
Discovery of 22° Halos
The discovery and research on 22° halos can be attributed to many scientists and observers throughout history who have studied atmospheric optical phenomena. However, it is challenging to pinpoint a single individual who can be credited with their discovery, as these halos have likely been observed for centuries.
Many ancient civilizations and cultures had knowledge and observations of various atmospheric phenomena, including halos around the sun and moon. However, the systematic study and understanding of these phenomena have evolved over time with advancements in scientific knowledge and instrumentation.
In the modern era, atmospheric scientists, meteorologists, and researchers have contributed significantly to the study of atmospheric optical phenomena, including 22° halos. They have conducted observational studies, performed measurements, and developed theoretical models to better understand the physics behind these phenomena.
The understanding of 22° halos and other atmospheric optical phenomena continues to evolve as new research and observations are conducted. Scientists and researchers around the world contribute to ongoing studies, which enhance our knowledge of these fascinating natural phenomena.
References and Resources
In addition to the 22° Halos, 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, Sun Dogs, Cathedral Floor, Rising Road, Moving Coils, Upside Down Rainbows