Physical Geography: Lecture Physical Geography: Lecture 2 2 EARTHEARTH

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?

What does Earth look like?What does Earth look like?

EratosthenesEratosthenes managed to figure out, in managed to figure out, in 247 B.C., Earth’s circumference247 B.C., Earth’s circumference

Eratosthenes’ calculation:

28,738 miles (46,250 km)

Earth’s actual polar circumference:

24,860 miles (40,008 km)

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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 an it’s an oblate ellipsoidoblate ellipsoid

Earth is NOT ROUND!!!Earth is NOT ROUND!!!

Why isn’t it a sphere?Why isn’t it a sphere? Centrifugal forceCentrifugal force

(It’s why the spin cycle in your washing (It’s why the spin cycle in your washing machine gets the extra water out of machine gets the extra water out of your clothes)your clothes)

Centrifugal ForceCentrifugal Force

Rotation vs. RevolutionRotation vs. RevolutionBoth create a bulge Both create a bulge

around the middle of around the middle of the planetthe planet

RotationRotation• Earth spinning in Earth spinning in

placeplace

Centrifugal ForceCentrifugal ForceRevolutionRevolution

• Earth’s orbital movement around the sunEarth’s orbital movement around the sun

Do you know where you are?Do you know where you are?

<< Quick! Stand up! >>

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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.

A Polynesian map showing wave patterns in the Pacific Ocean

Great Circles and Small CirclesGreat Circles and Small Circles

Another important piece of the navigation puzzle…Another important piece of the navigation puzzle…

Great CirclesGreat CirclesThe shortest distance between any two points on a globe lies along a great circle arc

Distortion of the Great Circle ArcDistortion of the Great Circle Arcon a Flat Mapon a Flat Map

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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 them Meet at the poles (distance between them

shrinks)shrinks)• Prime MeridianPrime Meridian is the primary reference is the primary reference

line (0º)line (0º)• International Date Line lies roughly along International Date Line lies roughly along

the 180º meridianthe 180º meridian

Latitude and LongitudeLatitude and Longitude

Why is Longitude a Problem?Why is Longitude a Problem?““The sun, moon, and planets pass almost The sun, moon, and planets pass almost

directly overhead at the Equator. Likewise the directly overhead at the Equator. Likewise the Tropic of Cancer and the Tropic of Capricorn, Tropic of Cancer and the Tropic of Capricorn, two other famous parallels, assume their two other famous parallels, assume their positions at the sun’s command. They mark the positions at the sun’s command. They mark the northern and southern boundaries of the sun’s 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 Any sailor worth his salt can gauge his latitude well enough by the length of the day, or latitude well enough by the length of the day, or by the height of the sun or known guide stars by the height of the sun or known guide stars above the horizon….The measurement of above the horizon….The measurement of longitude meridians, in comparison, is tempered longitude meridians, in comparison, is tempered by time…., [requiring] precise knowledge of the by time…., [requiring] precise knowledge of the hour in two different places at once….”hour in two different places at once….”

--Dava Sobel, --Dava Sobel, LongitudeLongitude

Figuring Out Your LongitudeFiguring Out Your Longitude

Earth rotates on its axis, one rotation Earth rotates on its axis, one rotation every 24 hours. The circle of Earth’s every 24 hours. The circle of Earth’s circumference is 360circumference is 360, so: , so:

360360 = __ hours = __ hours1515 = __ 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 mi lat. = 49 mi (79 km) (79 km) 9090 = 0 mi = 0 mi (0 (0 km)km)

Figuring Out Your LongitudeFiguring Out Your LongitudeYou need to know:You need to know:

The time back home (or some other known port)The time back home (or some other known port)The time aboard shipThe time aboard ship

Reset each day at noon (when the sun is at its Reset each day at noon (when the sun is at its zenithzenith))

What’s the time difference?What’s the time difference?Every hour of difference = 15Every hour of difference = 15 of longitude of longitude

Can you do it?Can you do it?If your clock is set two hours earlier than the time at your home port to If your clock is set two hours earlier than the time at your home port to

the east, then your ship must be ___the east, then your ship must be ___ west of your home port. west of your home port.

(Extra credit: If you’re at the equator, what’s your actual (Extra credit: If you’re at the equator, what’s your actual distance from home?)distance from home?)

The real problem facing the navigators? They didn’t have wristwatches!The real problem facing the navigators? They didn’t have wristwatches![Three cheers to John Harrison in 1761!][Three cheers to John Harrison in 1761!]

Time, Time, Time…Time, Time, Time…

Our way of organizing time is directly related Our way of organizing time is directly related to lines of longitudeto lines of longitude

Check this out…Check this out…

Fiji Is #1!!!Fiji Is #1!!!

In The ZoneIn The Zone

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)Beijing, China?