The rarest clouds on Earth were spotted by sky watchers in parts of western US, Europe and Canada over the weekend providing a vibrant display that has not been seen in about 15 years.Known as noctilucent, these clouds were glowing in the sky just after the sun moved below the horizon, Mail Online reported. Noctilucent clouds (NLCs) form in the mesosphere, which is at altitudes of around 80 kilometers & 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 below the horizon.There's really nothing else quite like them,& the National Weather Service office in Seattle wrote on social media, noting that these are the &most vivid displays of noctilucent clouds& that have been seen in decades in the area.Mail Online reported the clouds appear with electric blue and silver streaks and are typically spotted at latitudes of 45 and 80 degrees in the northern and southern hemispheres.The post Rare glow-in-the-dark clouds seen over US, Canada and Europe first appeared on Ariana News.