Determining Longitude with a Clock - Watch and Learn #58

3-Second Blueprint (English)

1. Navigators found latitude by sighting the Sun's maximum zenith angle at local solar noon—or Polaris at night—using a sextant and seasonal tables.
2. Calculating east-west longitude required comparing observed local solar noon against prime-meridian reference time kept aboard on a chronometer.
3. Because Earth rotates 15 degrees per hour, even small daily clock drift compounded over ocean voyages into dangerous positional errors at sea.