Causes of sunsdog
The most common nebulosity occurs on either side of the Sun, with an angle of 22° centered on the observer between the Sun and the nebulosity. When the Sun is on the horizon, the angle is 22°, but as the Sun’s elevation angle increases to 60°, the angle between the Sun and cumulus almost doubles to 45°.
This can be explained by the fact that when ice crystals with a hexagonal shape and a diameter of more than 30 micrometers fall from the air, they refract sunlight like a prism as they fall horizontally. The shape of the flock is like a ring, but the shape of the flock appears on either side or one side of the sun, as if it were a reflection of the sun. In the figure, the angle between the sun and the flock increases with increasing altitude of the sun.
When the Sun is on the horizon, the angle is 22°, but when the Sun is at 60°, the angle is 45°. When the Sun’s altitude is above 60°, the sun does not appear in the sky. They are best seen at sunrise or sunset when the sun’s rays are refracted at 22°. The lower the sun’s altitude, the more clearly it is seen. The color of the cumulus clouds varies from red when they are close to the sun to a bluer color when they are farther away from the sun.
The 22° sunsdog circle can be described as the refraction of sunlight within a falling hexagonal ice cube with its center axis parallel to the perpendicular direction. The side closer to the sun is reddish in color, and the faint white horizontal arc at the sun’s altitude is called the parhelic circle, although small fragmentary circles are more often seen than complete parhelic rings.
When caused by the moon, they are called paraselenic circles. They are caused by the reflection of light from the vertical faces of ice crystals, such as large hexahedral plates, which also form parhelia and paranthelia.
What is a cluster?
There is a mysterious optical phenomenon in the sky. It’s a beautiful shape called a halo. It’s easier to understand if you call them sun or moon clusters. It’s a ring of light that surrounds the sun or moon. Was it a mystery of nature? In ancient cultures, they were called nimbus. It is said to have originated from the rainbow of the sun god.
Halos are caused by
Halos are an optical phenomenon caused by ice crystals. Ice crystals have a hexahedral structure, which makes them very similar to prisms. When light passes through an ice cube, the ice cube reflects and disperses light at the same time. Therefore, the cause of halo is the refraction and reflection of light by the ice cube. Depending on the angle of the light, you can see a 22° cloud, a 46° cloud, and a sunburst, as shown in the image below.
In general, clouds appear much more frequently than rainbows. On average, you can see them twice a week in Europe and the United States. There are several types of optical phenomena caused by ice, including halos, of which the 22° radius circle and sun dogs are the most frequent.
Based on the frequency of HALO observations, the 22° group occurs approximately 100 times per year. The table below shows the average number of observations per year based on 10 years of observations at the HALO Institute in Germany. This is the flock we see most often. However, there are several reasons why the 22° cluster is more common than the 46° cluster in the same group. First is the quality of the ice crystals.
Cloud crystals sometimes reduce the clarity of clusters. For example, the tip of an ice crystal blocks the light rays that form the 46° cluster, making it difficult to see the complete shape of the 46° cluster. The second is due to differences in the size and alignment of the ice crystals. For clusters to appear, ice crystals must be aligned in the correct shape. Larger ice crystals, larger than 0.1 mm, tend to be well aligned but imperfect.
The third reason is large clusters and dispersed color. Some clusters are so large that they appear scattered and faint. A 46° cluster is at least six times weaker than a 22° cluster.
Sun dogs or parhelia are also refractions caused by ice crystals. However, their appearance is very different from halos. Parhelia are formed by plate crystal ice crystals with a diameter of more than 30 micrometers. While the shape of a halo is like a ring, the shape of a nebula appears on either side of the sun, as if it were a reflection of the sun. In the figure, the angle between the sun and the nebula increases as the sun’s altitude increases.
When the Sun is on the horizon, the angle is 22°, but when the Sun is at 60°, the angle is 45°. When the Sun’s altitude is above 60°, the sun does not appear in the sky. They are best seen at sunrise or sunset when the sun’s rays are refracted at 22°. The lower the sun’s altitude, the more clearly it is seen.