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Noctilucent clouds are extremely rare, very high clouds that are usually only seen in the summer night sky. They are particularly visible at dawn or dusk (around the same time when the brightest stars become visible), look wispy, luminescent and bluish or silvery.
Noctilucent clouds form when water vapor freezes around specks of dust. They appear to shine brightly in the night sky when they are illuminated by the sun shining on them from below the horizon.
Scientists say that climate change is making noctilucent clouds more visible. That’s because increasing greenhouse gas emissions from human activity create more water vapor, which enhances the visibility of noctilucent clouds. They were always there, we just couldn’t see them as often before.
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