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    Re: Art and Navigation
    From: Paul Hirose
    Date: 2015 Apr 27, 23:12 -0700

    On 2015-04-27 11:36, Carly Butler wrote:
    > I
    > knew I should have an artificial horizon, but I actually thought  it
    > wasn't that important (!) and that I could get an approximate location
    > that wouldn't be so far off.
    You don't need an artificial horizon to have fun with a marine sextant.
    In fact, I think "fun" and "artificial horizon" are mutually exclusive!
    Fiddling around with a bowl of fluid is not my cup of tea. Never tried a
    mirror artificial horizon, but it doesn't seem attractive. If I wanted
    to dink with a bubble and leveling screws, I'd use one of my theodolites.
    With just the sextant you can be spontaneous. For instance, in the
    middle of writing the first paragraph I noticed it was twilight. Grabbed
    my Astra and went outside. No stars yet, but there was the gibbous Moon
    high in the sky. I had to go to the fence and shoot toward my porch. I'm
    not used to that direction, but took a hurried sloppy shot anyway,
    estimating where the horizon ought to be.
    According to a subsequent calculation, what I judged to be horizontal
    was actually 3° above the horizon. Not too good, but not terrible
    considering the conditions. When I'm shooting in a familiar direction
    where I know some reference points, I can get within a degree.
    With an AH at night, the darker the better. But when you have to
    estimate the horizon, darkness in a mixed blessing. It helps star
    visibility, but your horizon references are harder to see. You have to
    compromise and shoot in twilight, just like a sailor.
    One mistake I made tonight - forgot to remove the scope. With an
    estimated horizon the reduced accuracy doesn't justify a scope. In fact,
    removing the scope *increases* accuracy because it's so easy to shoot
    with both eyes open and thereby get a better sense of horizontal. It's
    also much less trouble to find the body.
    In some cases the scope helps with star visibility. But for the Sun,
    Moon, and planets, it just makes observing more difficult and less accurate.
    Of course "less accurate" applies to all observations with an estimated
    horizon. But I find the satisfaction of an accurate observation is
    relative to the equipment and techniques in use.

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