Nacreous clouds are usually seen shining in the darkening sky after sunset or before sunrise.
These, imaged by Kalinka Irina Martin Iglesias over Tunhovd fjord in Nore og Uvdal, Norway on 20th January 2008, were so bright that they were visible in daytime. In fact, Kalinka used sunglasses to reduce the light!
More images of the Scandinavian 19-20th January display 1,2.
©Kalinka Irina Martin Iglesias, shown with permission.