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?