Determining Latitude and Longitude

One of the questions that I wondered while transcribing was how did they determine the Latitude and Longitude. They used a sextant to determine latitude and a chronometer to find the longitude. The sextant was invented in 1731. Using a sextant is pretty complicated. To use it you need to do some calculating, refer to tables, and you ned have some knowledge of the sky and earth. To find the latitude, you need to measure the angle between the horizon and the sun at its highest point, usually about noon. Then you refer to the table, and it will tell you what latitude the sun should be over that day.
















Every hour the earth rotates 15 degrees. Therefore using a chronometer, greek roots chronos which means time and met which means measure, you can find your longitude. After referring to your tables, you could do some simple math and determine what your longitude is at that time of day. Then using the rate at which the earth is spinning and the rate at which you are travelling it is not terribly difficult to figure out what longitude you are at.

















Check out this link for some more information on ancient navigation and sailing techniques.
http://www.pbs.org/wgbh/nova/ancient/secrets-of-ancient-navigators.html

Check out this one for more information on finding latitude and longitude.
http://www.pbs.org/wgbh/nova/shackleton/navigate/escapenav.html

Now it makes sense that they seem to skip so many Latitudes and Longitudes in the Logbook. If they do not use the sextant at noon then they cannot get an accurate reading and also it is a lot of work for  Thomas Scullen Master so if he had other things to do that day then he might not have been able to get around to it.