Timetable of NLC and Solar Altitudes - Basic Geometry

Just geometry for now. Will work seasonal effects in later.
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Lat/Lon: W is neg! Height (m): Screening Height (km): or

Screening height: The lower atmosphere is thick/opaque enough to cast a shadow, turning NLC dark that would otherwise be in sunlight if considering only the solid earth as the limiting factor. A clean airmass would have a screening height closer to 13km.
Code will break for southern hemisphere. Mobile app being considered. Other ideas welcome.
Project initiation: late September 2018