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On 11 Dec 2004 at 13:18, Fred Hebard wrote:

> Errors for stars east and west of the moon often cancel each other out.
>   Would not paired observations such as those made by Thompson similarly
> cancel the error in longitude?

Yes, when he takes two observations on either side of the moon then most
of these dates would reduce his error considerably. Taking the sun, of
course, would give the full error of the position of the moon. Two sights
on the same night is not all that common in Thompson's notes, perhaps once
in 7-10 lunars (but I'd have to really check to say for sure).

For the Rocky Mountain House longitudes, if you just look at those
measurements where two occur on a single date (and so have stars on both
sides of the moon), then Thompson's average is only about 12' out and the
deviation is less. I wonder if he only used those in his own average? When
I was looking at his data last summer I couldn't figure out why the value
he used for the position of Rocky Mountain House didn't correspond to the
average of all his sights. Perhaps he was selective. I'll have to go back
and look at this.

Ken Muldrew.

   

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