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The "cut" of the LOPs derived at Howland Island on July 2, 1937 for the sun and
moon lines varied between 59 degrees at 1830 Z to 125 degrees  at 2100 Z and
back down to 69 degrees at 2400 Z which would provide acceptable "cuts" for
accurate celestial fixes at anytime during that period. These cuts were not all
the prefect 90 degrees but all are well above the minimum 15 degree cut stated
in "Weems" 1938 edition on page 281.

There has previously been a concern stated that the moon was too high in the
sky to be measured with the sextant as it was above 75 degrees when they
arrived in the vicinity of Howland. However, by 1945 Z its altitude was below
70 degrees and got progressively lower as the day progressed while the altitude
of the sun got higher. Both of their altitudes stayed below 70 degrees between
1945 Z and 2400 Z (presumably the tanks dry point); both were below 65 degrees
2015 Z through 2300 Z; below 60 Degrees 2030-2230 Z; and below 55 degrees
2100-2200 Z. We also know that Noonan was able to measure the altitude of the sun 
while crossing the Atlantic when it's altitude was 75 degrees so he should have 
been able to shoot the moon at a similar altitude.


Some have suggested that the 157-337 LOP was not a sun line at all but was based
on an observation of the moon. The only time of the day on July 2, 1937 in the 
vicinity of Howland that a moon shot would have produced a 157-337 LOP was between
1620 and 1626 Zulu or 0450 and 0456 Itasca time, well before the arrival of 
NR16020 in that vicinity. This makes it very unlikely that AE was referring to 
a moon LOP.

I doubt that any flight navigator has ever shot Venus during the day, it's
difficult enough for a surface navigator. And since Venus is right next to the sun
an LOP from Venus crossing the sun line would not provide a reasonable cut for a fix,
your example gives a one degree cut.

But the moon should have been able to provide a fix.

gl








Greg Rudzinski wrote:
> Ron,
>
> At 1745Z sunrise at Howland Island on July 2, 1937 the celestial
> bodies available in addition to the Sun would have been Venus Hc 44�
> 42' Az 068� for a LOP of 158�/338� and the Moon Hc 72� 01' Az 043� for
> a LOP of 133�/313�. Venus would have been visible through the entire
> day with a clear sky. I believe FN purposely selected July 1 & 2 to
> maximize celestial opportunities for his morning arrival at Howland
> Island. The aircraft could have easily adjusted course to provide the
> best view for an observation. FN would have surely thought of these
> things ahead of time. There was no need for a very low altitude Sun
> observation.
>
> Greg
>
> On Nov 30, 3:38 pm, Ronal

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