NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Ted Gerrard's book
From: Michael Daly
Date: 2007 Nov 19, 01:38 -0500
From: Michael Daly
Date: 2007 Nov 19, 01:38 -0500
coralline algae wrote: > I see in other messages on this list that occultations were used > as a sort of almanac, a way to mark a point in time, when > clocks were still not accurate enough to for surveying or > navigation. Here is where I will shamelessy speculate that > almanacs of that time may have stated something like there > will be an occultation of a specific ecliptic star by the moon at > approx midnight? Think of a lunar occultation as a special case of a lunar distance - where the distance is precisely 0.00 degrees. Otherwise, the method is essentially the same and requires the same level of precision in an almanac table that specifies the location of the moon relative to the stars. Appulses are similar but there is more room for error - the star will not "turn off" and provide a well-defined point in time. Halley's method can only be as accurate as his lunar position knowledge. No one published tables at that time (as Maskelyne did after 1767). There was the raw data that was coming out of Flamsteed's observations and other observers that may have been accumulating data. Newton and Halley published Flamsteed's data without his permission in 1712 but what Halley used in the 1699 timeframe I don't know offhand. Mike --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---