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Subject: RE: [Nml] Lunars
From: Daniel K. Allen (Visual C++) (danallen@XXX.XXX)
Date: Tue Feb 16 1999 - 12:49:45 EST
Here is a rough set of steps:
Measurements:
Measure height of moon h1, height of sun h2 lower limbs. (t-n min)
Measure distance d1 between nearest limbs. (t)
Measure height of moon h3, height of sun h4 lower limbs. (t+n min)
Calculate:
Ham = (h1+h3)/2 - dip + SDm = apparent height of moon
Has = (h2+h4)/2 - disp + SDs = apparent height of sun
Da = d + SDm + SDs = apparent distance
cos(Da)=sin(Ham)*sin(Has) + cos(Ham)*cos(Has)*cos(Z) solve for Z
Hm = Ham - refraction + parallax
Hs = Has - refraction + parallax
cos(d)=sin(Hm)*sin(Hs) +cos(Hm)*cos(Hs)*cos(Z) solve for d
Lookup:
Determine declinations of moon, sun from a nautical almanac.
Best guess for latitude.
Calculate LHA of moon, sun:
cos2(LHA/2) = cos1/2(dec+lat+Z)*cos1/2(dec+lat+Z) / cos(dec)*cos(lat)
Bowditch has details on this in all editions up through the year 1912 or so.
I got these details from an out of print book called "Navigation Afloat: A
Manual for the Seaman" by Alton B. Moody, 1980. The book only devotes one
page to the topic, and it is distilled above.
There is a book available from http://www.celestaire.com by Stark, Bruce
entitled "Tables for Clearing the Lunar Distance and Finding G.M.T. by
Sextant Observation", Lant-horn Press Eugene, OR, 1995,1997 that has more
details.
This should be part of a Navigation FAQ. Do we have one?
Dan
-----Original Message-----
From: JMason@XXX.XXX]
Sent: Tuesday, February 16, 1999 8:24 AM
To: navigation@XXX.XXX
Cc: JMason@XXX.XXX
Subject: [Nml] Lunars
Has anyone ever seen a reference to an actual procedure (book, calculator,
or
computer program) for the celestial navigation solution for longitude called
"luners"?
My understanding is one starts with the time at which one or more of the
navigation stars is occulted by the moon, and traditionally performs a
massive
(hours to solve without calculators) spherical trigonometry solution which
yields position. But how does one do it? Even Bowditch is silent.
There is another solution using the moons of Jupiter, but I don't think this
is the "luners" used by master mariners in the last century.
John Mason
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