<P> Latitude was calculated by observing with quadrant or astrolabe the altitude of the sun or of charted stars above the horizon, but longitude is harder . </P> <P> Amerigo Vespucci was perhaps the first European to proffer a solution, after devoting a great deal of time and energy studying the problem during his sojourns in the New World: </P> <P> As to longitude, I declare that I found so much difficulty in determining it that I was put to great pains to ascertain the east - west distance I had covered . The final result of my labours was that I found nothing better to do than to watch for and take observations at night of the conjunction of one planet with another, and especially of the conjunction of the moon with the other planets, because the moon is swifter in her course than any other planet . I compared my observations with an almanac . After I had made experiments many nights, one night, the twenty - third of August 1499, there was a conjunction of the moon with Mars, which according to the almanac was to occur at midnight or a half hour before . I found that...at midnight Mars's position was three and a half degrees to the east . </P> <P> By comparing the positions of the moon and Mars with their anticipated positions, Vespucci was able to crudely deduce his longitude . But this method had several limitations: First, it required the occurrence of a specific astronomical event (in this case, Mars passing through the same right ascension as the moon), and the observer needed to anticipate this event via an astronomical almanac . One needed also to know the precise time, which was difficult to ascertain in foreign lands . Finally, it required a stable viewing platform, rendering the technique useless on the rolling deck of a ship at sea . See Lunar distance (navigation). </P>

Which of the following is the best example of drawing center lines