Can the suns position in the sky not be estimated by the time of day? Therefore an hour glass could track the Sun from daylight to dark? As long as East and West can be defined?
Ahhh ... that's the big problem, isn't it? Defining longitude is not easy. The development of precise, portable chronometers was driven by the need for such devices to determine longitude.
Can the suns position in the sky not be estimated by the time of day? Therefore an hour glass could track the Sun from daylight to dark? As long as East and West can be defined?Of course. That is what makes navigation by the stars and sun possible. The whole point of the sunstone is to compare the observed elevation of the sun to what it ought to be at any given observation.
The sun's elevation at (for example, high noon) is known for every latitude for every day of the year and that data can be set out in tables to be published for the use of navigators.
Then the navigator can observe the elevation of the sun at its zenith and consult the table to see his latitude.
Longitude is a tougher proposition. For that, you need to have a highly accurate clock (a navigator's marine chronometer) and a much more complex set of tables to set out elevations for the major stars in your hemisphere, again in relation to the time of day and the day of the year.
The clock would be set for an exact time at a known reference point on the earth (for example at Greenwich Observatory) and the clock must maintain its accuracy throughout the voyage.
The accuracy of the position fix will depend on the accuracy of the clock and the accuracy of the sextant that is used to obtain several stars elevations and the skill of the navigator to take accurate measurements.
Observing three stars wull produce curves lines on a chart of the surface of the globe together they make a "cocked hat" within which is the navigator's calculated position.
The greater the accuracy of the clock and the sextant and the accuracy of the navigator's obseravation, the smaller is the cocked hat.
Latitude was not a major problem for the Vikings. Longitude was a problem.
Caveat: I am grossly over-simplifying here