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Gary LaPook added:
The 157/337 LOP could have been obtained by a sun sight taken anytime
within an hour of sunrise since the sun's azimuth stayed at 067º for
more that an hour after sunrise. It is very unlikely that Noonan would
have taken just a single sight when the sun was at low altitude (such as
right at sunrise) due to the greater possible error with low altitude
observations. He would have been able to take a series of sights to
ensure when he had arrived on the LOP through Howland.

Paul Hirose wrote:

>
> The speed line they obtained from the Sun rising nearly dead ahead
> should have revealed any serious headwind, and Noonan could have shot
> course lines out his side window during the night.
>
>


 LaPook adds:
 in fact a rhumb line only adds about two miles to the great circle
since the course is essentially along the equator.

> Using those coordinates, my GPS agrees with the planning sheet data to
> practical accuracy. (The speeds and distances on that sheet are in
> statute miles.) But look at those 15 waypoints on a great circle track!
> It seems a pointless refinement for a flight so close to the equator. I
> would eliminate all those little course changes, and plan the flight so
> Earhart could fly a constant magnetic course all the way from Lae to
> Howland.
>

LaPook adds:
 I would have expected him to do whatever was necessary to get that moon
observation including opening the door and hanging outside if necessary.
More practically, the plane had a flat glass window installed on the
left side for astronomical observations and the moon would have been
visible from the left side of the aircraft since it was north of the
plane. Using the same type of sextant that Noonan used, an A-5, it is
possible to take observations up to 80º by holding the sextant within an
inch of a vertical window since the index prism is located at the front
of the sextant. In fact, I just shot the sun at 69º 46' through my
hallway window. He could have had AE slip the plane for the two minutes
necessary to take an observation if he needed greater altitude range and
could have had her change heading also if necessary.

The moon passed NORTH of Howland at 1837Z and its altitude was 76º 56'
at that point since its declination was 13º52' North.  At the time of
their last transmission at 1912 Z the altitude of the moon was 74º 27'
and the azimuth of the moon was 328º T .
There has 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.

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 perfect 90 degrees but all are perfectly acceptable. It would have
been the perfect 90º at 1902Z when the moon was at 336º and the sun at
066º and their altitudes were 75º 36' and 16º 46' respectively. It would
also have been the perfect 90º at 2325Z when their azimuths were 285º
and 015º.

> Though I'm skeptical about the lunar parallax theory, the author of that
> page does have a good point: the Moon was available. But its altitude
> may have been too high for convenient use. When Earhart said, "we must
> be on you," it was about 65° high at Howland. I don't know if Noonan
> would have been able to shoot it.
>
> By 2100Z the situation would have improved, with the Sun and Moon both
> about 45° up, and a 125° split in azimuth.
>
>> I
>
>

   

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