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    Re: Celestial in the thin air!
    From: Frank Reed
    Date: 2020 Jun 9, 12:10 -0700

    Alexander, you wrote:
    "I did this: change the elevation in the F6 dialog"

    Aha! Thank you. I had a vague memory of something that would change the appearance of the atmosphere with altitude, and this does so. But does it change the refraction with altitude? My quick tests say no, but I could be doing it wrong. I tried a star quite close to the horizon, and it seems to show the same refraction regardless of the physical altitude of the observer. I can test by turning the atmosphere off entirely.

    You added that you "noticed that the horizon does not go down (also, there is a limit of 200km for the elevation). Stellarium takes a changing density into account, but not the change in geometry."

    No change in geometry, or in navigation terms, there's no dip. It's annoying, but there has been a long-standing "design principle" in the Stellarium community that there should be no dip, even at very high altitudes like the ones you entered, where the dip amounts to more than ten degrees. The primary purpose of the variable observer altitude is to get topocentric artificial satellite altitudes correct. It appears to handle this correctly, when judged by zenith distances, and even shows proper changes in the altitude of the Moon. Pick a time when the Moon is low in the sky, stop time, then climb to an altitude of 100,000m, e.g. The Moon drops by about 0.9', with refraction turned off, as it should (100km/384000km is the ratio of altitude to mean distance, multiplied by 3438 gives minutes of arc, about 0.9).

    Frank Reed
    Clockwork Mapping / ReedNavigation.com (more online classes starting in two weeks)

       
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