| At these times the clouds are visible and are therefore referred to as noctilucent clouds. |
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| Evidence of these changes comes from sightings of noctilucent clouds, very unusual clouds seen only in polar regions and known to be in the mesosphere. |
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| Ice crystal clouds, called noctilucent clouds, occasionally form in the upper mesosphere. |
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| This would permit the study of so-called noctilucent clouds, the highest in the atmosphere, which are thought to have an important role in climate change. |
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| May's black ash from the Eyjafjallajökull eruption in Iceland might just have a silver lining... Look north at twilight this month, and you may find yourself seeing one of the sky's most ghostly phenomena: noctilucent clouds. |
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| White Knight Two and SpaceShipTwo, says Dr Stern, could fly more experiments to noctilucent clouds in six months than NASA has managed in 40 years. |
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| Based on historical records of significant noctilucent cloud development in the skies over Europe following the event, some scientists contend that a comet caused the explosion. |
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| Maciej created a time-lapse video from his pictures, putting them together into a stunning twominute skyscape of noctilucent clouds over a glowing night sky. |
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| Nacreous and Noctilucent clouds form not in the part of the atmosphere in which we live, but much higher up, in the stratosphere and mesosphere. |
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| Noctilucent clouds hover some 50 miles above the Earth's surface. |
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