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Frank Reed writes-

>Shall I add Maskelyne's paper from the Philosophical Transactions of 1764
>describing how to clear a lunar to my web site?

Yes,please.

Lunar distances were computed in four steps, as I understand it.

First the position of the Moon was calculated, in terms of ecliptic
latitude and ecliptic longitude, at noon and midnight, using Mayer's
predictions. These were VERY complex calculations, so the largest possible
time-interval was chosen, of 12 hours.

Then interpolations were made between those positions, to get the Moon's
position at 3-hour intervals. Because the moon's lat and long vary so
wildly, linear interpolation wasn't sufficient. Instead, a second-order
interpolation was done, which took the curvature into account, by looking
at four successive positions of the Moon.

Then these 3-hour Moon positions were converted to declination and right
ascension,

Then appropriate bodies (Sun or stars) were chosen, East and West of the
Moon, near the Moon's path and with an appropriate angular distance from
the Moon for easy measurement with a sextant. Then the angle between the
Moon and the star was calculated from the decs and RAs.

The same task was given to two "computers", working away from Greenwich,
who were not allowed to know of each other's existence. Only if their
predictions agreed were they accepted.

On one occasion the computers managed to identify each other and compared
notes in secret, which led to their instant dismissal.

Derek Howse, "Greenwich Time and the Longitude", is good on this.

One of Maskelyne's computers, William Wales, accompanied Cook, as
astronomer, on his second voyage.

George.



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