>Sun is very very bright
>Clouds are not solid
The kind of cloud that is most apparent at sunset, is thin, wispy, and not entirely opaque. The light from the sun can very easily shine through the cloud, making it seem that the cloud disappears behind the sun. When in fact, it simply shines so brightly behind it that the cloud appears translucent.
This can be easily replicated, with the right materials.
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Then why would some clouds appear in front of the sun, as well as behind as in this picture?
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Not every cloud is exactly the same as we all know. It could very well be a mixture of clouds, some blocking out the suns light, whilst some do not, and are instead lit up so brightly from behind that they appear the way they do. I'm by no means an expert in this field, but this is a very likely hypothesis.
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