NavList:

   

Reply

George Huxtable wrote of the precision astrolabe [NavList 10131]

>  How much greater than 60�, then, was the
>recommendation, which would determine the time-lapse between the two events,
>and also affect the achievable precision?
>
>George.

A very good question George, and I am afraid I do 
not have an answer. If, as the body transits the 
meridian, the transit altitude of the body is 
very close to 60�, then the altitude is varying 
very slowly through the sensitive angle and there 
is a lack of precision in deciding exactly when 
the two images coincide. So it is difficult to 
get an accurate longitude. If the transit 
altitude is a lot higher than 60�, the body moves 
relatively quickly in altitude through 60� - both 
applying and separating from its transit across 
the meridian - giving good precision for those 
times. But then, as the bodies are increasingly 
observed towards the East and the West at large 
azimuth differences, latitude becomes difficult 
to measure accurately. In practice, a number of 
stars of differing declinations would be 
observed, consistent with the star's transit altitude being greater than 60�.

Geoffrey.





--~--~---------~--~----~------------~-------~--~----~
NavList message boards: www.fer3.com/arc
Or post by email to: NavList@fer3.com
To , email NavList+@fer3.com
-~----------~----~----~----~------~----~------~--~---

   

Reply