Hi Brent, Would that it were that simple. Longitude still requires an absolute, not relative time fix. You still need to know the time and longitude from Greenwich. Sunrise and noon are relative to local time. Discovering longitude for many years perplexed astronomers and navigators to the point of insanity. Dava Sobel's book "Longitude" is a great read.
Roger Bailey -------------------------------------------------- From: "Brent" <bren...@verizon.net> Sent: Tuesday, October 12, 2010 2:59 PM To: "Roger W. Sinnott" <rsinn...@post.harvard.edu>; "Sundial List" <sund...@rrz.uni-koeln.de> Subject: Re: Light Based Geolocation > The way I understand the geolocation device is that dawn rises at the > same time along different longitudes. If you know what time sunrise is > and how long the day is on a particular day you know your latitude as > well as your longitude. > > On a deserted island, the time of sunrise is the number of hours > before high solar noon....and maybe half way between sunrise and sunset. > > This manual seems to indicate these concepts: > http://www.wildlifecomputers.com/Downloads/Documentation/WC-GPE%20Suite%20Manual.pdf > > It's because of the tilt of the earth? > > > Roger W. Sinnott wrote: >> Brent, >> >> I think you could determine your latitude this way, but not your >> longitude. >> For the longitude, you would need some way to relate your local sunrises >> and >> sunsets to the local time at some known longitude, such as that of >> Greenwich. >> >> In other words, the geolocation tagging gadget must carry a time-of-day >> clock from a known longitude. This is the same as the age-old longitude >> problem that all mariners faced. >> >> -- Roger >> >> >> ----- Original Message ----- >> From: "Brent" <bren...@verizon.net> >> To: "Sundial List" <sund...@rrz.uni-koeln.de> >> Sent: Tuesday, October 12, 2010 5:05 PM >> Subject: Re: Light Based Geolocation >> >> >> >>>So I am marooned on a island with nothing but I might be able to >>>determine a few things that I could write on a message in a bottle >>>that would help my rescuers determine my exact location. >>> >>>By careful sunrise observation I could determine the solstices. >>>Now I have a calendar. >>> >>>I know dawn to dawn is 24 hours so I could make a clock with a washed >>>up bottle filled with sand and measure/mark what comes out in one day. >>> >>>Then I could cut that sand in half for 12 hours and half again for 6 >>>hours and half again for 3 hours and then thirds for one hour. >>>Now I have an hour clock. >>> >>>Now I can measure the hours of daylight from dawn to dusk on the >>>solstice and send that in the bottle and my rescuers will be able to >>>determine my latitude and longitude. >>> >>>Of course I would have to say northern or southern solstice but that's >>>easy because we know the sun rises in the east. >>> >>>Would this be enough information? >>> >>>thanks again; >>>brent >>> >>>--------------------------------------------------- >>>https://lists.uni-koeln.de/mailman/listinfo/sundial >>> >>> >> >> >> --------------------------------------------------- >> https://lists.uni-koeln.de/mailman/listinfo/sundial >> >> > > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial > --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
