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    Re: Lewis and Clark lunars: more 1803 Almanac data
    From: Ken Muldrew
    Date: 2004 Apr 21, 16:51 -0600

    On 21 Apr 2004 at 17:33, Frank Reed wrote:
    > Ken M you wrote:
    > "I had another look at a star chart over lunch and found a small, dim,
    > red star at the bottom of Orion's bow (PI 6 Orion) with an 1803 right
    > ascension of 4h 48m 23.5s, dec 1? 24' 5.7". I stuck that into my
    > spreadsheet where I was comparing the cleared distance with the true
    > distance for various stars (in my post of this morning) and it appears
    > to be our mystery star. "
    > Though this is possible, I'm skeptical for a couple of reasons. First,
    > this is a very faint star. That bright gibbous moon would make it
    > extremely difficult to see.
    I know. I have a hard time believing for this very reason as well.
    > What worries me more is that this may have
    > become a case of a solution that fits the data by mere chance. Your
    > standard of solution was to seek a star that would fit the distance
    > and rate of change of the observations to within a few minutes of arc.
    > There are two patches of sky that would do this, as a matter of
    > mathematical necessity. How large are those patches? What is the
    > probability that you will find a star brighter than magnitude 5.0 (or
    > some other limit) merely by chance in one of those patches? Indeed, is
    > there a star in the patch on the opposite side of the ecliptic that is
    > as bright as Pi 6 Ori?
    I didn't check too thoroughly but I couldn't find a star above
    magnitude 5.0 that was even close. There are certainly no bright
    candidates in that part of the sky.
    > All that said, I think it's still a possibility.
    The data looks genuine to me; I just can't see it being due to sloppy
    work (aside from inexperience).
    > Is there some
    > methodological error that would have led to this star instead of
    > Aldebaran? Do any of the stars near Pi 6 Ori make a pattern that might
    > be mistaken for the Hyades (possibly inverted) by an inexperienced
    > observer? Aldebaran is one of the easiest lunars stars to identify
    > because of the distinctive pattern around it, and that pattern is
    > well-described in Moore/Bowditch etc.
    I cannot see anything around it that would cause one to make that
    mistake. I don't often see Pi 6 Ori very often because I live on the
    North edge of a large city, so the stars in the South are usually
    pretty washed out. It's only when I'm out of town that I can see
    Orion's bow, so I'm really not familiar with it.
    I had another thought last night that made more sense, but I was a
    bit worried about burdening the list with more of my undisciplined
    speculation. Since I'm already replying, I'll add it here as well.
    Betelgeuse is almost in a direct line from the moon to Pi 6 Ori at
    the time in question, and the brightness and colour make it an
    obvious candidate for such a mistake. But it's just way too close to
    the moon; 15?, in fact. Exactly 15?. Now I can't quite figure out
    what error would lead to the captains recording distances that were
    off by 15?, but for some reason the fact that there are no minutes or
    seconds in the error makes me think it's possible. If I clear the
    distance based on the assumption of Betelgeuse, here's what I get:
    GMT     clr'd d true d
    5.094   59.784  44.407
    5.323   59.832  44.508
    5.493   59.892  44.599
    5.589   59.896  44.636
    5.643   59.975  44.669
    5.694   59.986  44.693
    7.267   60.477  45.437
    7.362   60.543  45.492
    7.419   60.521  45.511
    7.490   60.522  45.545
    7.525   60.547  45.570
    7.571   60.546  45.583
    This is actually what I was looking for in the first place. A star
    that could be mistaken for Aldebaran that gave a relatively constant
    error when the cleared and true distances were compared. There is
    still a bit of a slope to the error, but because of the difference in
    distance, I'm not as concerned about it as I was with stars that were
    actually at the measured distance. Since I'm clearing the distance
    based on a measured distance that's 15? too large, I could be
    introducing a systematic error that causes that slope.
    So here's a potential solution, but where do you get a 15? error?
    Ken Muldrew.

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