Talk:John Hadley

Untitled

Hi,

I beleive there is a minor inaccuracy in this article.

"If the position of the object on the sky and the time of the observation are known, it is easy for the user to calculate his latitude."

If you determine the elevation of the sun on the sky at local noon (highest elevation that day), the lattitude can be calculated without timing (I mean independent source of exact GMT) information. However, if the observation was made in arbitrary time, you can not calculate the lattitude of the observer. A line of position can be derived, but this is not certainly paralell of lattitude (better say, in most cases it is not). In this case several celestial objects should be observed, and the position of the observer (vessel) is at the intersection of the lines of position.

I suggest to change "If the position of the object on the sky and the time of the observation are known, it is easy for the user to calculate his latitude." to "If the positions of the objects on the sky and the time of the observations are known, the user can resolve his position on the Earth.".

Any comment?

Jozsef

Perhaps they meant to say "longitude" and left out a lot of info. I think that a more general statement about determining position should replace the existing statement. A link to sextant with a comment on that article's explanation of use of the instrument coupled with a link to celestial navigation for how position is determined would suffice. Michael Daly 16:55, 13 September 2007 (UTC)

Gregorian Telescope priority?

I have found info that Hooke made a Gregorian telescope in the 1600s, so the comment on Hadley being the first is in doubt. Michael Daly 16:55, 13 September 2007 (UTC)

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