This document discusses the lost art of celestial navigation using the stars. It explains how sailors were able to determine their latitude and longitude at sea before modern navigation tools. Some key methods mentioned include using Polaris to determine latitude, observing the positions of stars near the eastern or western horizon over multiple nights to calculate longitude, and using a Mariner's Nocturnal instrument to determine local time by the angles between stars like Polaris and Ursa Major.

1. Sailing by Starlight: the Lost Art of Celestial NavigationAndrew Thaler

2. Do you know where you are?

3. Finding your way home

4. Finding your way homeSouthern SkyNorthern Sky

5. Finding your way homeHow do you travel in a straight line?Latitude hookMust be calibrated to a specific locationPolaris above the loop, head southPolaris below the loop, head northKamalWhy does this work?

6. Determining LatitudePolaristan θ = x/yθ = LatitudeXθHorizony

7. Determining LatitudeAccurate to within 1 Degree1 degree of latitude = 60 minutes1 minute = 1 nautical milePolaris is 430 light years away2.5 X 1015 milesIf surveyors were as accurate as Polaris - 0.0000000002 inchesIf Polaris was as accurate as a surveyors - 4,000,000,000 miles

8. Latitude is θCross staffQuadrantAstrolabeOctantSextant

9. LongitudeThe X-Prize of the millenniumNo accurate method until 19thcentury3 puzzle piecesRotation of the earth = 15o per hourTime the sun peaks at prime meridian = 1200Time (GMT) the sun peaks at your location

10. Relative LongitudeNot very accurate!Find a star near the eastern or western horizonMeasure the altitude of that star at the same time every nightChanges in degrees correspond to movement east or west2 CaveatsNeed to correct for latitudeNeed to know what time it is

11. What time is it?The sky is a clock, tooMariner’s NocturnalMeasures the angle between Polaris and Ursa Major or Ursa Minor

12. Using the NocturnalAn analog computer

13. Set the dial to the date

14. Sight Polaris through the center hole