Today’s Very Important Word: Uniformitarianism“The present is the key to the past” How old is the Universe? How old is planet Earth? How do we know? 2
What does Earth look like? Eratosthenes—managed to figure out, in 247 B.C., Earth’s circumference Eratosthenes’ calculation: 28,738 miles (46,250 km) Earth’s actual polar circumference: 24,860 miles (40,008 km) 3
Guess what??? Earth is NOT ROUND!!! Earth’s polar circumference: • 24,860 miles (40,008 km) Earth’s equatorial circumference: • 24,902 miles (40,076 km)Earth is not a sphere… …it’s an oblate ellipsoid 4
Why isn’t it a sphere? Centrifugal force (It’s why the spin cycle in your washing machine gets the extra water out of your clothes) 5
Centrifugal ForceRotation vs. Revolution Both create a bulgearound the middle of the planetRotation • Earth spinning in place 6
Centrifugal ForceRevolution • Earth’s orbital movement around the sun 7
Do you know where you are? << Quick! Stand up! >> << Quick! Stand up! >> 8
How do you find your way if you don’t have any navigational instruments? What if clouds obscure the sky? Song: “Stand” by R.E.M. 9
A Polynesian mapshowing wavepatterns in the PacificOcean 10
Great Circles and Small CirclesAnother important piece of the navigation puzzle…
Great Circles The shortest distance between any two points on a globe lies along a great circle arc
Distortion of the Great Circle Arc on a Flat Map
The Geographic Grid Latitude (x-axis) • Parallels (never touch) Always the same distance apart • Equator is the primary reference line (0º) Longitude (y-axis) • Meridians Meet at the poles (distance between them shrinks) • Prime Meridian is the primary reference line (0º) • International Date Line lies roughly along the 180º meridian 14
Why is Longitude a Problem? “The sun, moon, and planets pass almost directlyoverhead at the Equator. Likewise the Tropic of Cancerand the Tropic of Capricorn, two other famous parallels,assume their positions at the sun’s command. Theymark the northern and southern boundaries of the sun’sapparent motion over the course of the year...” “Any sailor worth his salt can gauge his latitude wellenough by the length of the day, or by the height of thesun or known guide stars above the horizon….Themeasurement of longitude meridians, in comparison, istempered by time…., [requiring] precise knowledge ofthe hour in two different places at once….” --Dava Sobel, Longitude 16
Figuring Out Your LongitudeEarth rotates on its axis, one rotationevery 24 hours. The circle of Earth’scircumference is 360°, so: 360° = __ hours 15° = __ hour(s) 1° = __ minutesNote: The distance between lines of longitude varies with latitude 0° = 69 mi (111 km) 45° lat. = 49 mi (79 km) 90° = 0 mi (0 km) 17
Figuring Out Your LongitudeYou need to know: The time back home (or some other known port) The time aboard ship Reset each day at noon (when the sun is at its zenith)What’s the time difference? Every hour of difference = 15° of longitudeCan you do it?If your clock is set two hours earlier than the time at your home port to the east, then your ship must be ___° west of your home port.(Extra credit: If you’re at the equator, what’s your actual distance from home?) The real problem facing the navigators? They didn’t have wristwatches! [Three cheers to John Harrison in 1761!] 18
Time, Time, Time… Our way of organizing time is directly related to lines of longitude Check this out…
Ready for a quick review? 1. What’s the name of the theory that states that “the present is the key to the past”? 2. Who came up with a fairly accurate measurement of Earth’s size in 247 B.C., using only geometry? 3. What is the name for the shape of our planet? 4. What is centrifugal force? What two phenomena cause the centrifugal forces that affect Earth’s shape? 5. The shortest distance between two points on a globe lies along a ___________________.
6. The primary reference line of latitude (0°) is ______________. The primary reference line of longitude (0°) is _______________.7. What’s the most important instrument to have if you need to figure out your longitude? How do you figure it out?8. True or False? Time zones follow lines of longitude, with exactly 7.5° on either side of the line.9. If you flew from San Francisco to Sydney, Australia today, on what day would you arrive?
10. What time is it RIGHT NOW in: a) New York City? b) Hilo, HI? c) St. Paul, MN? d) Fairbanks, AK? e) Denver, CO?
HomeworkStudy for Quiz #1 Make photo copies of the map Write in the featuresCheck the class blog. Watch the videos (orlook for some of your own to share withthe professor!)