In Northern Earth 135 (autumn, 2013) there is a little piece with the title, 'what would our ancestors make of this?' which set me thinking. Noctilucent clouds are ripples in the sky, in the mesosphere (50 miles upwards) and they tend to be visible in the first hour after sunset (during the twilight zone). They form on the smoke trails of meteors burning up as they enter the atmosphere leaving a layer of particles on which moisture can form reflective crystals.
At www.rasc.ca there is a pdf on noctolucent cloud formation and the connection with meteors – calling them luminous 'night' clouds high in the atmosphere thought to be from when rising water vapour condenses on meteoric particles filtering down from space – therefore not just meteors but even the smallest grains of cosmic dust. These clouds are only visible in the twilight when they occupy a sunlit portion of the atmosphere and the Sun is situated 6 to 16 degrees below the horizon. They can't be seen in daylight.
At http://science.nasa.gov/science-news/science-at-nasa/2012/07aug_meteorsm… … also has plenty of information on this peculiar phenomenon, describing them as electric-blue ripples and pale tendrils. The site has a video that explains how meteor smoke makes noctilucent clouds. It seems that ash from some volcanoes has the same effect – quoting the Krakatoa eruption of 1885. Ash from the volcano created beautiful sunsets around the world and looking at the sky in the evening became a popular pastime (they say). The noctilucent clouds appear after sunset, however – but were an integral part of the whole experience. The piece goes on to say these phenomena, once confined to Canada and Scandinavia, and other northern regions, have been spotted as far south as Colorado and Nebraska – and it is here blamed on climate change and specifically, the release of methane. Needless to say no actual evidence is presented – it is just a statement added to what was until that moment a scientific description of the phenomenon. I could just as easily respond by saying it also coincides with low activity on the Sun and a shrinking atmosphere – but that doesn't mean anything without some research.
See also www.spaceweather.com/nlcs/gallery2009_page13.htm which has some nice images of the phenomenon.
We began with – 'what would our ancestor have made of this?' It is an interesting thing to say. We have records of intense meteor showers, as recent as the 17th century AD, so how would this have affected translucent clouds. Would they have grown exponentially with the number of meteors, or the amount of cosmic dust. If the orbit of the Earth ploughed through a region of the sky dense with cometary remains, how would that have appeared to our forebears. What would they have made of it?