Noctilucent Clouds and you
Noctilucent Clouds (NLCs, also called Polar Mesospheric Clouds) are clouds made of extremely small ice crystals and are at the highest known altitude of any cloud structure around the Earth. They’re only visible during that post-sunset/pre-sunrise period where the observation site is dark, but the high altitudes are still illuminated by the over-the-local-horizon Sun.
The Aurora Borealis (or “Northern Lights”) light shows are the result of collisions of energetic charged particles with atoms in the high altitude atmosphere – I’ve not seen them in person, myself, but hope to one day!In the 1990s, we had some discussions and Flight Rule updates re: noctilucent clouds and Space Shuttle entry profile selections.
Since the phenomenon was still relatively unknown, or at least what the (quite literal) impacts of thin, high-altitude ice would have on a hypersonic Space Shuttle, we were directed to prioritize Shuttle entry profiles/directions so that we avoided (if possible) northerly approaches on high-inclination missions that would have taken us through areas with potential NLCs.