On Tue, Jan 24, 2012 at 3:16 AM, Attila Kinali <att...@kinali.ch> wrote: > On Tue, 24 Jan 2012 11:04:08 +0000 > "Poul-Henning Kamp" <p...@phk.freebsd.dk> wrote: > >> In message <20120124115848.312d60bd4fccce4f3e71c...@kinali.ch>, Attila >> Kinali w >> rites: >> >> >All this talk about telling the time using stars or the sun made me wonder >> >how did people tell what position their telescopes had back in the days >> >before GPS?
Sailingships and trade was what pushed this. At the time of Columbus he was able to know his latitude within a few 10s of miles but even after returning to Europe he did no know how far around the world he had sailed. Was it 1/3rd or 2/3rds? They had no way to know. The problem was that on one had a clock that should keep time well enough. They used hour glasses on board ship for short duration time keeping but those were of no use on a longer ocean crossing. Later they discovered the idea of common view of the moons of Jupiter and they could measure the time from local noon some even on Jupitor while a person back home did the same thing. Later when he got back home they compare notes and then know the difference in longitude. Good ocean going clocks were still centuries away. But in the 1500's they could only know the location after the fact when they returned -- Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
