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• 1. Sailing by Starlight: the Lost Art of Celestial Navigation
Andrew Thaler

2. Do you know where you are?
Southern Sky
Northern Sky
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?
6. Determining Latitude
Polaris
tan = x/y
= Latitude
X

Horizon
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
Cross staff
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
Mariners Nocturnal
Measures the angle between Polaris and Ursa Major or Ursa Minor
12. Using the Nocturnal

• An analog computer

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