5. Finding your way home How do you travel in a straight line? Latitude hook Must be calibrated to a specific location Polaris above the loop, head south Polaris below the loop, head north Kamal Why does this work?
7. Determining Latitude Accurate to within 1 Degree 1 degree of latitude = 60 minutes 1 minute = 1 nautical mile Polaris is 430 light years away 2.5 X 1015 miles If surveyors were as accurate as Polaris - 0.0000000002 inches If Polaris was as accurate as a surveyors - 4,000,000,000 miles
8. Latitude is θ Cross staff Quadrant Astrolabe Octant Sextant
9. Longitude The X-Prize of the millennium No accurate method until 19th century 3 puzzle pieces Rotation of the earth = 15o per hour Time the sun peaks at prime meridian = 1200 Time (GMT) the sun peaks at your location
10. Relative Longitude Not very accurate! Find a star near the eastern or western horizon Measure the altitude of that star at the same time every night Changes in degrees correspond to movement east or west 2 Caveats Need to correct for latitude Need to know what time it is
11. What time is it? The sky is a clock, too Mariner’s Nocturnal Measures the angle between Polaris and Ursa Major or Ursa Minor
Step 1 – figure out what hemisphere you’re inPlenty of ocean to get lost in
Celestial pole – lucky if you’re in the north, polaris is at the poleLearn your landmarks – the two bears in the north, the southern cross in the southFind the southern pole by drawing a line from acrux and the tip of the cross and between agena and rigelcentaurus, lines intersect at the southern celestial pole
