It's pretty easy to be certain that you are looking at the sun and the moon. The moon was also available that morning and its placement in the sky provided a line of position running mainly east-west so would let Noonan know how far north and south they were just like the 157-337 LOP (mainly north-south) let them know how far east or west they were. Because of the moon, and the fact that Itasca reported clear skies to the south, Noonan taking a sight on the moon would have prevented them from flying very far south of Howland and would have kept them from ending up on Gardner.
That's a pretty good argument that he did not "shoot the moon" because he didn't reach Howland and he apparently did reach Gardner.
The Itasca radio log records "partly cloudy" report from Earhart at 1623 Z (look at the 0453 Itasca time entry in Itasca number 2 radio log) so even if Noonan had been prevented earlier from getting star sights by "overcast" conditions you can bet you last dollar that they were going to maneuver the plane in that area to allow Noonan to get a star fix around 1623 Z.
The Itasca Radio Log has always been interpreted that way but the raw log preserved by Bellarts is not that clear. The log records that at 04:53 Itasca time, the operator sent Earhart the weather on 3105 in both morse code and voice ("fone"). Earhart seems to have "stepped on" that transmission and the operator typed on the same line (HEARD EARHART (PART CLDY). He then went back and typed dashes over the (PART CLDY), hit the carriage return, and continued the dashes through about half of the next line. Why? (The dark line under HEARD EARHART was added much later, probably by Bellarts.)Where the dashes a mistake? Did he change his mind about what he had heard? I don't know but there is certainly room to question whether Earhart said "partly cloudy."
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But radio log 2 was made as a cleaned up copy of the raw log very shortly later. The person typing up log 2 had the opportunity to ask Bellarts at that time, when the facts were the most clear in his head, what Bellarts actually meant by what he had typed in the raw log. Since log 2 does not have dashes over the "part cldy" entry, Bellarts must have clarified this as being what he had heard.
Any other explanation must include that Bellarts was smoking dope at the time and just dreamed up that entry in the raw log.
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It just occurred to me that it may actually have been Bellarts that typed up log 2 so he would have known what he had heard as logged on the raw log when he typed up log 2.
gl