也许是月亮反光@。@
很抱歉，我的摄影水平不行，加上傍晚光线不是很好，所以比较暗。谁能解释这种现象？
也许是月亮反光@。@ |
http://www.ddhw.com/listo.aspx?topic_id=21&msg_id=5672&level_string=0z02&page=1 |
1. The phenomenon is caused by the diffraction (衍射) of light with suspended ice crystals in the air, not the refraction (折射). 2. There is no need for the ice crystals in an ordered structure, disordered structure (must be crystals) still can give a diffraction pattern (typically, diffraction rings). (Like in a powder sample X-ray diffraction experiment.) 3. The double "“幻日”, observed in the diffraction ring is dependent to the observer's position. |
I can see the sun halo from xyh's photo, which can be identified by the colorful rainbow-like edge on the right of the photos. One sundog appears quite brightly near the halo. |
Sunlight is not a single color light (i.e., light band with narrow wavelength range), instead it is a combination of light with a broad wavelength range, which includes all wavelengthes of the visible range (roughly from 400 nm to 850 nm). It is because this, and also the Bragg's diffraction equation: nλ = 2d sinθ (wavelength dependent) a hue (rainbow phenomenon) should be observed at the diffraction circle due to the different wavelengthes in the Sunlight. In fact, the observed hue and the double "Sun dog" is a proof of diffraction, since reflection and refraction can only give one fake image, not the symmetrically distributed double ones. Unfortunately the Wikipedia is wrong too. That is why it can not be confidently used as a reliable reference resource in Academia. |
I don't think that you can rule out refraction/reflection based on the color spectrum and number of sundogs. As we know, rainbow is exactly a result of refraction. Since I don't know much about the observational details of sundogs, I would not rule out diffraction as well. See materials below which I found from UIUC. I believe they have good creditbility. Sundogs, also known as mock suns or "parhelia", are a pair of brightly colored spots, one on either side of the sun.
Sundogs are visible when the sun is near the horizon and on the same horizontal plane as the observer and the ice crystals. As sunlight passes through the ice crystals, it is bent by 22 degrees before reaching our eyes, much like what happens with 22 degree halos. This bending of light results in the formation of a sundog. The difference between sundogs and halos is the preferential orientation of the ice crystals through which the light passes before reaching our eyes. If the hexagonal crystals are oriented with their flat faces horizontal, a sundog is observed. If the hexagonal crystals are randomly oriented, a halo is observed.
=============== BTW, CAN DIFFRACTION EFFECT EXPLAIN THE VERTICAL COLOR BAR LIKE PATTERNS ON EACH OF THE SUNDOGS? (SEE BELOW) |
I'll use diagrams to explain it. Meanwhile, please check the definition of "refraction, reflection, diffraction and scattering". Sorry for the inconvenience. |
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