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2. Do you know where you are?
3. Finding your way home
4. Finding your way home
5. Finding your way home
How do you travel in a straight line?
Must be calibrated to a specific location
Polaris above the loop, head south
Polaris below the loop, head north
Why does this work?
6. Determining Latitude
tan = x/y
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
The X-Prize of the millennium
No accurate method until 19th
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
Need to correct for latitude
Need to know what time it is
11. What time is it?
The sky is a clock, too
Measures the angle between Polaris and Ursa Major or Ursa Minor
12. Using the Nocturnal
13. Set the dial to the date 14. Sight Polaris through the center hole 15. Rotate the arm until it lines up with the head of Ursa Major