Noctilucent Cloud

At a height of around 200,000 feet, in the atmospheric layer known as the mesosphere, these rare clouds are higher than any other. At these altitudes there is very little moisture. They are occasionally observed in late summer evenings in the higher latitudes of the planet, when the sun has set at ground level, but is still shining higher in the atmosphere. They appear as thin streaky clouds with a light, sometimes, silvery luminescence.