For the first time in my life, I identified the NLC (Noctilucent clounds) at around 02:15 am local time in Letterkenny on 1st July 2017. I drove towards the outskirts of the town to get a better view free from any obstruction from the city lights and got these beautiful pictures. Night clouds or noctilucent clouds are tenuous cloud-like phenomena in the upper atmosphere. They are the highest clouds in Earth's atmosphere, located in the mesosphere at altitudes of around 76 to 85 kilometres. These clouds can be observed only during local summer months and when the Sun is below the horizon for the observer, but while the clouds are still in sunlight. Noctilucent roughly means night shining in Latin.
Noctilucent clouds are not fully understood and are a recently discovered meteorological phenomenon. For example, during my school days these clouds were not even mentioned among the cloud's classifications in the science text books, and I don't think that they made into the curriculum even now. It may be because of the fact that this recent discovery is not well understood and is only visible in the summer months at latitudes between 50° and 70° north and south of the equator. These are becoming increasingly visible, and at times, man made rockets also causes these clouds to appear, and at times due to meteor breaking up in the atmosphere and from it's debris.
You can read more about these clouds in Wikipedia here https://en.wikipedia.org/wiki/Noctilucent_cloud