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    Re: Visibility at rising and setting
    From: Thomas Schmidt
    Date: 2000 Apr 25, 11:09 AM

    George Huxtable wrote:
    > What I'm asking is whether any of you enjoys clear enough skies that they
    > can observe stars or planets, even Venus at its brightest, right down to
    > being able to time a sudden moment of extinction as it sets below the
    > horizon.
    The right person to ask this is probably Prof. Brad Schaefer of Yale,
    who has devised detailed models of atmospheric extinction, drawing on
    a large database of observations. See for example this abstract:
    http://www.aas.org/publications/baas/v30n4/aas193/354.htm ,
    > [23.02] Celestial Visibility for Astronomy History
    > B. E. Schaefer (Yale)
    > The application of astronomy to history often requires detailed calculations
    > of the visibility of celestial objects. Recent advances have greatly improved
    > the accuracy, scope, and ease for making celestial visibility calculations.
    > I will detail my recent results for heliacal rise dates and directions,
    > extinction angles for rising stars, the dates of lunar crescent visibility,
    > and the size of the ubiquitous refraction variations low on the horizon. Some
    > simple resulting statistics will also be mentioned. Since the theory is complex
    > and the observations are many, the results will be presented in a handout as
    > graphs that cover most cases, references to the original articles, and complete
    > computer programs. I hope to provide workers with the tools required to support
    > their research.
      Thomas Schmidt                  e-mail:     schmidt@hoki.ibp.fhg.de

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