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On 02/06/2014 02:06, Frank Reed wrote:
> Earlier this evening, Hanno Ix and I were discussing a method for finding 
longitude that was used historically by land-based astronomers. You time the 
difference between the transit of the Sun and the transit of the Moon (either 
the leading or trailing limbs of each body). How accurately could you do this 
with simple tools and basic math today? Does it depend on an exact meridian 
observation, or if we're a degree or two out of line with the true meridian 
(but the same for both bodies) can we still get an accurate longitude? And 
can anyone point us to a write-up of this technique from the early 19th 
century? Is it in Chauvenet somewhere? Observations like this were certainly 
used to get longitudes of observatories in remote locations in the era before 
the telegraph. Anyone else interested in resurrecting this technique? --just 
for fun, of course!
>
> -FER

"Hints to Travellers" is a good book to see what methods were used to
find absolute time in temporary or small observatories around the end of
the 19th century. This method is not mentioned. The Moon occulting a
star is cited as the best method for determining absolute time.

This sounds like a fun project though, and ideal for a theodolite. I
will give it a bash when the next sunny day comes along and the Moon is
"above the earth" diurnally.

Geoffrey Kolbe.

   

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