This week ends with the noctilucent clouds captured by astronaut Alex Gerst on board ISS.

Credit: Alex Gerst, ESA, NASA

Noctilucent clouds, or night shining clouds, are tenuous cloud-like phenomena in the upper atmosphere of Earth. They consist of ice crystals and are only visible during astronomical twilight. They are most often observed during the summer months at high-altitude areas. They are the highest clouds in Earth’s atmosphere, located in the mesosphere at altitudes of around 75-85km. They are too faint to be seen in daylight, and are visible only when illuminated by sunlight from below the horizon while the lower layers of the atmosphere are in Earth’s shadow.

The noctilucent clouds captured from the ground is as follows.

Credit: Wikipedia

Reference: Alex Gerst’s Tweet
See earthview photo gallery with web-globe: LiVEARTH