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# GEOG 100: Lecture 02--Earth!

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### GEOG 100: Lecture 02--Earth!

1. 1. Physical Geography: Lecture 2Physical Geography: Lecture 2 EARTHEARTH EARTHEARTH
2. 2. 22 Today’s Very Important Word:Today’s Very Important Word:  UniformitarianismUniformitarianism ““The present is the key to the past”The present is the key to the past” How old is the Universe?How old is the Universe? How old is planet Earth?How old is planet Earth? How do we know?How do we know?
3. 3. 33 What does Earth look like?What does Earth look like?  EratosthenesEratosthenes—managed to figure out,—managed to figure out, in 247 B.C., Earth’s circumferencein 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)
4. 4. 44 Guess what???Guess what???  Earth’s polar circumference:Earth’s polar circumference: • 24,860 miles (40,008 km)24,860 miles (40,008 km)  Earth’s equatorial circumference:Earth’s equatorial circumference: • 24,902 miles (40,076 km)24,902 miles (40,076 km) Earth is not a sphere…Earth is not a sphere… ……it’s anit’s an oblate ellipsoidoblate ellipsoid Earth is NOT ROUND!!!Earth is NOT ROUND!!!
5. 5. 55 Why isn’t it a sphere?Why isn’t it a sphere?  Centrifugal forceCentrifugal force (It’s why the spin cycle in your washing machine(It’s why the spin cycle in your washing machine gets the extra water out of your clothes)gets the extra water out of your clothes)
6. 6. 66 Centrifugal ForceCentrifugal Force Rotation vs. RevolutionRotation vs. Revolution Both create a bulgeBoth create a bulge around the middle ofaround the middle of the planetthe planet RotationRotation • Earth spinning in placeEarth spinning in place
7. 7. 77 Centrifugal ForceCentrifugal Force RevolutionRevolution • Earth’s orbital movement around the sunEarth’s orbital movement around the sun
8. 8. 88 Do you know where you are?Do you know where you are? << Quick! Stand up! >><< Quick! Stand up! >> << Quick! Stand up! >><< Quick! Stand up! >> 88
9. 9. 99 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.
10. 10. 1010 A Polynesian map showing wave patterns in the Pacific Ocean
11. 11. Great Circles and Small CirclesGreat Circles and Small Circles Another important piece of the navigation puzzle…Another important piece of the navigation puzzle…
12. 12. Great CirclesGreat Circles  The shortest distanceThe shortest distance between any two pointsbetween any two points on a globe lies along aon a globe lies along a great circle arcgreat circle arc
13. 13. Distortion of the Great Circle ArcDistortion of the Great Circle Arc on a Flat Mapon a Flat Map
14. 14. 1414 The Geographic GridThe Geographic Grid  LatitudeLatitude (x-axis)(x-axis) • ParallelsParallels (never touch)(never touch)  Always the same distance apartAlways the same distance apart • EquatorEquator is the primary reference line (0º)is the primary reference line (0º)  LongitudeLongitude (y-axis)(y-axis) • MeridiansMeridians  Meet at the poles (distance between themMeet at the poles (distance between them shrinks)shrinks) • Prime MeridianPrime Meridian is the primary referenceis the primary reference line (0º)line (0º) • International Date Line lies roughly alongInternational Date Line lies roughly along the 180º meridianthe 180º meridian
15. 15. 1515 Latitude and LongitudeLatitude and Longitude
16. 16. 1616 Why is Longitude a Problem?Why is Longitude a Problem? ““The sun, moon, and planets pass almost directlyThe sun, moon, and planets pass almost directly overhead at the Equator. Likewise the Tropic of Canceroverhead at the Equator. Likewise the Tropic of Cancer and the Tropic of Capricorn, two other famous parallels,and the Tropic of Capricorn, two other famous parallels, assume their positions at the sun’s command. Theyassume their positions at the sun’s command. They mark the northern and southern boundaries of the sun’smark the northern and southern boundaries of the sun’s apparent motion over the course of the year...”apparent motion over the course of the year...” ““Any sailor worth his salt can gauge his latitude wellAny sailor worth his salt can gauge his latitude well enough by the length of the day, or by the height of theenough by the length of the day, or by the height of the sun or known guide stars above the horizon….Thesun or known guide stars above the horizon….The measurement of longitude meridians, in comparison, ismeasurement of longitude meridians, in comparison, is tempered by time…., [requiring] precise knowledge oftempered by time…., [requiring] precise knowledge of the hour in two different places at once….”the hour in two different places at once….” --Dava Sobel,--Dava Sobel, LongitudeLongitude
17. 17. 1717 Figuring Out Your LongitudeFiguring Out Your Longitude Earth rotates on its axis, one rotationEarth rotates on its axis, one rotation every 24 hours. The circle of Earth’severy 24 hours. The circle of Earth’s circumference is 360circumference is 360°°, so:, so: 360360°° = __ hours= __ hours 1515°° = __ hour(s)= __ hour(s) 11°° = __ minutes= __ minutes Note: The distance between lines of longitude varies with latitudeNote: The distance between lines of longitude varies with latitude 00°° = 69 mi= 69 mi (111 km)(111 km) 4545°° lat. = 49 milat. = 49 mi (79 km)(79 km) 9090°° = 0 mi= 0 mi (0 km)(0 km)