To find the position of a ship or aircraft by celestial navigation, the navigator uses a sextant to take a 'sight' to measure the apparent height of the object above the horizon, and notes the time from a marine chronometer. The object's position is then looked up in the Nautical Almanac for that particular time and after allowance for refraction, instrument error and other errors, a position circle on the Earth's surface is calculated.
Navigation by Sextant:
http://www.pbs.org/wgbh/nova/shackle...escapenav.html
online nautical almanac:
http://www.tecepe.com.br/scripts/AlmanacPagesISAPI.isa
Find your Longitude game:
http://www.pbs.org/wgbh/nova/longitude/findgame.html