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    Re: Celestial in the thin air!
    From: Frank Reed
    Date: 2020 Jun 5, 13:27 -0700

    Hello Suzanne. Glad to see you found the NavList message boards. As I said when you emailed, it's a helpful group.

    You asked Michael Jones:
    "can I make the program Stellarium show the view from 20,000 feet where the air is thin and cold?"

    If anyone else knows a better method, I apologize for my interruption, but I do know of one way to do this. In Stellarium, hit the F4 key on your keyboard. This will open the Sky and View Options dialog. On the Sky tab (first one up when the dialog opens), you'll see "Refraction/Extinction settings". You can lower the pressure in millibar to a very low level. This doesn't make the sky black in daylight, as it should, but it does reduce the refraction properly, in direct proportion to the pressure. In the troposphere, the density of the atmosphere falls with height at a rate of about 10% per kilometer (in a "cumulative interest", geometric growth sense, so at each km of altitude, it's 10% lower than the km just below it). The density of the air at the tropopause (bottom of the stratosphere, approx. 11km or 36,000 feet above sea level) is about 30% of the density at sea level. So if you use 300 mb pressure in Stellarium and leave the temperature unchanged, you should closely simulate the apparent refraction up there. I'm sure you can work out the pressure in mb for 20,000 feet equivalent yourself.

    Frank Reed
    Clockwork Mapping / ReedNavigation.com
    Conanicut Island USA

       
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