Strange clouds high in the atmosphere

There are strange clouds high in the atmosphere

http://spaceweather.com/nlcs/gallery2007_page7.htm

Here is a gallery of strange clouds that show up many times in the summer. First noticed in the 1800s after the great volcanic Krakatoa volcano explosion, they appear after sunset.
Here is a gallery of some of the best photos

(E.O.A.S.1) Read and compare 5 types of clouds as to shape, how high they form, appearance etc
http://australiasevereweather.com/techniques/moreadv/class.htm
(E.O.A.S.2 ) Compare/ contrats nocticlucent clouds to cumulus, cirrus, stratus or any 3 clouds.