An upside-down rainbow is a rare optical phenomenon known as a circumzenithal arc. An upside-down rainbow appears as an arc of colors in the sky, similar to a regular rainbow, but with the colors reversed and the arc positioned upside down.
If you are interested in learning more about Upside Down Rainbows, scroll down to read more about them.
Table of Contents
- What are Upside Down Rainbows?
- How do Upside Down Rainbows work?
- Some Similar Phenomenon
- References and Resources
What are Upside Down Rainbows?
An upside-down rainbow is a rare optical phenomenon known as a circumzenithal arc or an upside-down rainbow. It appears as an arc of colors in the sky, similar to a regular rainbow, but with the colors reversed and the arc positioned upside down.
Here are some key points about upside-down rainbows:
- Formation: Circumzenithal arcs are formed when sunlight passes through ice crystals in the atmosphere, typically cirrus clouds, at a specific angle. The ice crystals act as prisms, refracting and reflecting sunlight to create the arc.
- Location: Unlike regular rainbows that are seen near the horizon, upside-down rainbows are positioned higher in the sky. They occur directly overhead, or more precisely, centered around the zenith point.
- Colors: The colors of an upside-down rainbow are similar to those of a regular rainbow—red on the outer edge and violet on the inner edge. However, due to the inversion of the arc, the colors appear in reverse order.
- Brightness: Upside-down rainbows are often more vivid and intense than regular rainbows, as the sunlight is more concentrated and focused within the smaller arc.
- Rarity: While regular rainbows are relatively common, circumzenithal arcs are considered rarer due to specific atmospheric conditions required for their formation. They are more frequently observed in locations closer to the polar regions.
- Atmospheric Conditions: The presence of cirrus clouds, which consist of ice crystals, is crucial for the formation of upside-down rainbows. These clouds are thin and wispy and often indicate high-altitude weather systems.
- Angular Position: Upside-down rainbows are always positioned directly opposite the sun. Therefore, they are most commonly observed when the sun is lower in the sky, typically during morning or late afternoon hours.
- Halo Phenomena: Circumzenithal arcs are closely related to other halo phenomena, such as sundogs and halos around the sun or moon. These optical effects are caused by the interaction of sunlight with ice crystals in the atmosphere.
- Transient Nature: Upside-down rainbows tend to be short-lived and may only last for a few minutes. They require specific atmospheric conditions and the precise alignment of sunlight, ice crystals, and the observer’s position.
- Aesthetic Appeal: The beauty and unique nature of upside-down rainbows make them a captivating sight for those fortunate enough to observe them. They are often considered a delightful and fascinating natural phenomenon.
How do Upside Down Rainbows Work?
Upside-down rainbows, also known as circumzenithal arcs, are formed by the interaction of sunlight with ice crystals in the atmosphere. Here’s a step-by-step explanation of their formation:
- Sunlight: The process begins with sunlight. Sunlight consists of a spectrum of colors, including red, orange, yellow, green, blue, indigo, and violet.
- Cirrus clouds: Cirrus clouds, which are high-altitude clouds composed of ice crystals, play a crucial role. These clouds are often thin and wispy in appearance.
- Orientation of ice crystals: The ice crystals within the cirrus clouds must be oriented in a specific way. They need to be shaped like flat hexagonal plates with their faces parallel to the ground.
- Refraction and reflection: As sunlight passes through the ice crystals, it undergoes both refraction and reflection. Refraction occurs when light changes direction as it passes from one medium (air) to another (ice crystal). The hexagonal shape of the ice crystals causes the sunlight to refract at specific angles.
- Splitting of sunlight: The refraction of sunlight inside the ice crystals causes the sunlight to split into its component colors, similar to what happens in a regular rainbow. However, unlike a rainbow, the colors are split in a different way.
- Circumzenithal arc: The refracted and reflected sunlight forms an arc in the sky centered around the zenith point, which is the point directly overhead. This arc appears as an upside-down rainbow because the colors are reversed compared to a regular rainbow.
- Reverse color order: In an upside-down rainbow, the red color is on the outer edge of the arc, while violet is on the inner edge. This reversal of colors is due to the specific angles of refraction and reflection in the ice crystals.
- Angle of observation: To see an upside-down rainbow, the observer must be positioned with their back to the sun, and the arc will be directly overhead (centered around the zenith).
The formation of upside-down rainbows is dependent on specific atmospheric conditions, including the presence of cirrus clouds with oriented ice crystals and the position of the sun in relation to the observer. These factors contribute to the rarity of this optical phenomenon.
Some Similar Phenomenon
There are several atmospheric optical phenomena that are similar to upside-down rainbows (circumzenithal arcs) 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, at the same altitude as the sun. They are caused by sunlight passing through hexagonal ice crystals in the atmosphere, which act as prisms, refracting the light and creating a halo-like effect.
- Sun halos: Sun halos are circular rings of light that surround the sun. They are formed when sunlight passes through high-altitude cirrus clouds containing ice crystals. The ice crystals refract and reflect the sunlight, creating a halo effect.
- 22° Halos: 22° halos are similar to sun halos but occur around the moon instead of the sun. They are also formed by the interaction of moonlight with ice crystals in the atmosphere, resulting in a circular ring of light.
- Sun pillars: Sun pillars are vertical columns of light that appear above or below the sun. They are formed when sunlight reflects off flat ice crystals in the atmosphere, creating a pillar-like beam of light.
- Moonbows: Moonbows, also known as lunar rainbows, are rainbows that occur at night when the moon is nearly full. Moonlight is refracted and reflected by raindrops, creating a faint, usually color-pale rainbow.
- Iridescent clouds: Iridescent clouds are colorful clouds that display a range of vibrant colors. They are caused by diffraction and interference of sunlight as it interacts with water droplets or ice crystals in the cloud.
These phenomena are all fascinating optical effects resulting from the interaction of light and atmospheric particles. They often provide beautiful and captivating displays in the sky, offering a glimpse into the wonders of nature.
References and Resources
In addition to these Upside Down Rainbows, 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
