celestial navigation
Post on 18-May-2015
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Sailing by Starlight: the Lost Art of Celestial Navigation
Andrew Thaler
Do you know where you are?
Finding your way home
Finding your way home
Northern Sky
Southern Sky
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?
Determining Latitude
Polaris
Horizon
θ = LatitudeX
y
θ
tan θ = x/y
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
Latitude is θ
• Cross staff
• Quadrant• Astrolabe
• Octant• Sextant
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
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
What time is it?
• The sky is a clock, too
• Mariner’s Nocturnal
• Measures the angle between Polaris and Ursa Major or Ursa Minor
Using the Nocturnal
• An analog computer
• Set the dial to the date
• Sight Polaris through the center hole
• Rotate the arm until it lines up with the head of Ursa Major
Astronomers and Mariners
• None of these tools were invented for navigating
• We know where we are on earth because we wanted to know where we are in the universe
Questions?
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