Nacreous

FROM: GoodSearch on the Internet--
Nacreous clouds or mother-of-pearl clouds are difficult to document properly. Very often there is a dazzling brightness close to horizon while only a few degrees higher the sky is quite dark with clouds showing pastell colours. Capturing the bright part and the colours into same exposure is always a compromise. Nacreous cloud pastell colours are a bit like those in iridescence, but if sun is close to horizon or below it, then one is observing nacreous clouds. (Iridescence will be either gone or has turned into red and is indistinguishable from ordinary twillight clouds.) On my observing site I rarely see great nacreous clouds. Rather, they are peculiar twillight colours and long lasting red twillight well after cirrus clouds have turned black. Typical view at sunset is in he00652: milky and "soft", whitish veil. This stuff becomes visible only at sunset (or rise); it can be seen only about an hour prior to sunset (or after sunrise). Later this turns into red "twillight looking" cloud like in he01053 with an extremely brigh part close to horizon.