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Quote: ‘Pro tip for northern sky watchers: Look west 30+ minutes after sunset.’

May 27, 2021: Something unusual is happening at the top of Earth’s atmosphere. Noctilucent clouds (NLCs) are forming, and people are seeing them from the ground even though it is only May. Andy Stables sends this photo from the Isle of Skye, Scotland, taken May 26th:

The electric-blue ripples “were clearly visible to the unaided eye,” says Stables. “This is the earliest I have ever seen them here in Scotland.”

NLCs are Earth’s highest clouds. Seeded by meteoroids, they float at the edge of space about 83 km above the ground. The clouds form when summertime wisps of water vapor rise up to the mesosphere, allowing water to crystallize around specks of meteor smoke. The season for bright naked-eye NLCs typically stretches from June through August.

This year NLCs are getting an early start. We’ve already received multiple reports of sightings in Europe from latitudes as low as…