Tremendous display of noctilucent clouds became visible last night and at about 1:00am were at their best. Â Image taken with Canon 40D at 8 second exposure and ISO 160.
Noctilucent clouds are the highestÂ cloudsÂ inÂ Earth’s atmosphere, located in theÂ mesosphereÂ at altitudes of around 47 to 53 miles andÂ are composed of tiny crystals ofÂ water iceÂ up to 100Â nmÂ in diameter. They are normally too faint to be seen, and are visible only when illuminated by sunlight from below the horizon while the lower layers of the atmosphere are in theÂ Earth’s shadow.
More details on noctilucent clouds can be found here