Corona - 25.2.2017 at 13.30 Kerava Observation number 61508

• Lightsource of the phenomenon
• • Sunlight
• Common atmospheric phenomena
• • Iridescent clouds

    Iridescent clouds are clouds colored in the colors of spectra in the vicinity of a light source. The phenomenon is very common.

    Like a corona, a clouds of color are formed when light is scattered in small water droplets. Fineest colors are seen in cirrocumulus and altocumulus lenticularis-type clouds. The more mundane-looking color clouds, on the other hand, are lower clouds.

    Like coronae, color clouds usually occur only very close to the Sun. Their colors are more clearly visible through sunglasses.

    The word "iridescent clouds", clouds with colors, may sound the same as any colored cloud that exists. However clouds colored reddish by morning or evening dusk are not the same thing. The ridescent clouds specifically show the full color of spectrum. The iridescent clouds are not a synonym for the also colorful mother-of-pearl -clouds. These polar stratospheric clouds are a different phenomenon that occurs and very low winter temperatures hight in the atmosphere.

    

    Cloud iridescence on altocumulus lentocularis. Photo by Panu Lahtinen.

     

    

    Colors of spectrum on an altocumulus cloud. Image by Matti Helin.

    

    Iridescent Stratocumulus cloud. Photo by Panu Lahtinen.

     

    

    Sometimes it may be difficult to determine, if the colors on the cloud belong to a corona or cloud irridescence. This one could be marked with either one or both of the phenomena identifications. Image by Marko Myllyniemi.

  • Corona

    Corona (of the sun) is a colored ring or series of rings visible in the immediate vicinity of the light source. It can appear in both clouds and fog.

    Coronae are formed in very small drops of water. The size of the droplets affects the size of the corona ring. The smaller the droplets on average, the larger the circle is.

    With the water droplets being about the same size as each other, a series of strongly colored corona rings can be seen in the sky. When the droplet size is wide, only one ring with faint colors is visible.

    A corona can also be formed by small ice crystals in the upper clouds, but such coronas are very faint.

    The corona phenomena identification in Skywatch is intended for different kinds of corona rings that appear around the Sun. The coronae of the moon and planets have their own phenomena identification selections.

    Unlike halo rings, which are located apart from the Sun or the Moon, the perimeters form a uniform field of light in the immediate vicinity of the celestial body.

    

    Corona. Image by Ismo Luukkonen.

    

    Corona in the morning mist. Photo by Iida Pennanen.

     

    The distortion of the corona is caused by changing droplet sizes in the cloud. Imabe by Eetu Saarti. 

    

    A solar corona on a thick cloud. The lack of colors and suble changes in shades is hinting about wide range of droplets in different sizes. Photo by Marko Riikonen

    

    Feeble vaque corona. Image by Matias Takala.

     

    

    If the size of the droplets changes drasticly, the corona may appear strongly distorted. Photo by Aki Taavitsainen.

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