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    Re: Towards a basis for Bruce Stark's Tables
    From: John McKeel
    Date: 2003 Jan 3, 14:28 -0700
    RE: Towards a basis for Bruce Stark's Tables

    Fred,

    David Burch in the Starpath Celestial Navigation course has an article about using a mirror as an artificial horizon for night shots. He suggested using a professional level, a quality mirror and shimming the mirror with business cards. I understand people used to use mercury. I wonder if there are any other (less toxic) solutions for an artificial horizon that can be used at night?

    I've noticed the Davis artificial horizon is too small for many shots (This time of year at 33N that means before 9 or after 3.) The wind seems to conspire against my pie tins of oil (Don't ask...)

    Cheers,
    John McKeel
    Phoenix

    -----Original Message-----
    From: Fred Hebard [mailto:Fred{at}ACF.ORG]
    Sent: Friday, January 03, 2003 1:49 PM
    To: NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM
    Subject: Re: Towards a basis for Bruce Stark's Tables


    John,

    With the Davis Mark 3, I was using an artificial horizon, mostly a mirror, to shoot stars and planets.  I got so I was consistently within about 8 miles.  I determined, mostly with the Davis, but confirmed with the Husun, that inaccurate leveling of the mirror was the main culprit for the errors, by comparison to water or oil.  I was shooting at night from my deck and going inside between shots, so thermal effects were minimal: the index error of the Davis was fairly stable, and I got pretty good at checking and zeroing it out.  The lack of a telescope on the Davis Mark 3 is a disadvantage, as is the half mirror, half plain view, so that you never see overlapping images coming smoothly together.  A micrometer is also a necessity for precise movement of the index.

    Recently, I have been using a blackened pie pan with vegetable oil, which is less noxious than motor oil.  You don't want the oil so thin that surface tension distorts the surface, but it needn't be too thick, and needn't be colored dark.

    I expect the errors in my early shots were due to poor technique.

    Happy New Year!

    Fred

    --------------------------------------------------------------------------
    Frederick V. Hebard, PhD                      Email: mailto:Fred{at}acf.org
    Staff Pathologist, Meadowview Research Farms  Web: http://www.acf.org
    American Chestnut Foundation                  Phone: (276) 944-4631
    14005 Glenbrook Ave.                          Fax: (276) 944-0934
    Meadowview, VA 24361
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