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> This web page speculates that Amelia Earhart and Fred Noonan missed
> Howland Island because Noonan failed to correct for parallax when he
> shot the Moon:

I believe Noonan precomputed his sight reductions (that's what I would
do), so if he did make that mistake, it would have happened on the
ground. A blunder that big seems unlikely, though.

The 1939 edition of "Practical Air Navigation" (U.S. Department of
Commerce publication) has a Moon altitude correction table. It's much
like a modern table. You go down the left-hand column to find altitude,
then move across until you come to the column corresponding to the
Moon's parallax in altitude. The tabulated value at this point is the
combined parallax, refraction, and semidiametor correction.

This inventory of the plane's contents
http://www.tighar.org/Projects/Earhart/Documents/Luke_Field.html
includes a 1937 Nautical Almanac near the bottom. I don't see sight
reduction tables. Perhaps the
"Navigation Tables for Mariners and Aviators" served that purpose. No
sextant either. Maybe one of the navigators removed it.


The FAQ at the TIGHAR site has some pages on the navigation techniques
utilized on the flight:

http://www.tighar.org/forum/FAQs/Forumfaq.html

It says Fred Noonan had only one side window to make his celestial
observations. That's almost unbelievable.

Considerable space is devoted to explaining the meaning of the 157/337
line Earhart mentioned in one of her last transmissions. According to
the web site, it's a line of position obtained by noting the time of
sunrise as they flew toward Howland Island. (The Sun would have risen on
bearing 67° true; their inbound course was 77°.)

What I don't understand is why Earhart and Noonan would advance this LOP
and fly along it two hours later. A sunrise observation is the worst for
refraction error. Add the error due to advancing the LOP, and it's not a
pretty picture.

If I were the navigator, I'd prepare a table of the Sun's altitude vs.
time for Howland Island. Outbound from Lae, offset the course so the
plane will definitely miss Howland to one side, say to the south. When
my DR says we're on that Sun line, have Earhart turn left and put the
Sun on our beam. Now it's conveniently positioned for observing through
the side window. By comparing observed altitude to my table, I can see
whether we're left or right of the LOP, in near real time. Staying on it
should lead us to Howland. That's one of the standard airborne celestial
techniques for making landfall on an island in the ocean.

Noonan surely knew the method, but apparently didn't use it. I don't
know why. Cloud cover doesn't seem to have been serious. Itasca's deck
log says the sky was 3/10 obsured, and Earhart reported no trouble with
clouds.

The 157/337 line does make the lunar parallax theory less plausible. I
can't see Earhart and Noonan running back and forth along the old
sunrise LOP advanced to Howland Island if a newer LOP had been available.

   

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