Rare clouds that glow in the dark are seen in upper US, Canada and Europe 

The rarest clouds on Earth were spotted by sky watchers in parts of western US, Europe and Canada over the weekend a vibrant display that has not been seen in about 15 years.

Known as noctilucent, these clouds were glowing a stunning blue in the sky just after the sun moved below the horizon.

Reports of the eerie-looking clouds came from Oregon, Washington, Alberta, the UK and Denmark.

Noctilucent clouds (NLCs) form in the mesosphere, which is at altitudes of around 50 miles – making them the highest in Earth’s atmosphere.

The clouds consist of ice crystals that become visible during twilight when the sun is shining from blow the horizon.

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