Today. 03 Geodesy. Sphericity. Columbus. Eratosthenes. Pythagoras GEOG 101 8/16/16. Instructor: Pesses 1

Transcription

1 Today 03 Geodesy Part I Introducing Geography Geography 101 Physical Geography: Earth s Surface Landscapes M. Pesses, Antelope Valley College Geodesy Land Division Geodesy ô Science dealing with the measurement of the shape of & locations on the Earth Sphericity In 1492 Not the first to think Earth was round ô Accepted idea around AD 100 Columbus What shape is the Earth? Pythagoras Eratosthenes Greek Mathematician/ Philosopher ô BC ô Observed Earth was round ô But how? Librarian at Alexandria, Egypt ô 247 BC Instructor: Pesses 1

2 Syene, Egypt ô On Summer Solstice, sun cast no shadows ô Directly overhead 23.5 North So what? Eratosthenes knew that the sun was not directly overhead in Alexandria on that same day ô Proof that the Earth was round Measuring the Earth Measuring the Earth Eratosthenes found that the sun s rays were coming in about 7.2 off of 90 ô Roughly 1/50 of a 360 circle Measured the distance & multiplied by 50 ô His circumference, approx. 24,662 miles ô Today measured at 24,901 miles Sphericity But is the Earth REALLY round? Instructor: Pesses 2

3 Newton If the Earth is spinning on an axis ô Equator moves faster than poles Oblate spheroid ô Centrifugal force at the Equator Speed of Earth s Rotation Latitude Speed (kmph) Speed (mph) Nearest geographic point North Pole Seward, Alaska; St. Petersburg, Russia Chibougamau, Québec; Kiev, Ukraine Beijing, China; Valdivia, Chile Pôrto Alegre, Brazil; New Orleans, Louisiana Quito, Ecuador; Pontianak, Indonesia But Is it really an oblate spheroid? Geoid Geoid Literally means earth shaped An average sea-level assuming a fluid Earth with Earth s gravitational pull The rock of the Earth is bumpy Sea level is not the same everywhere ô Mean Sea Level (MSL) is seeking equilibrium with gravity Instructor: Pesses 3

4 GEOG 101 8/16/16 GPS Global Positioning System (GPS) cm accuracy Cardinal Direction Getting around our geoid Wind Direction The Compass Location How does one know where he or she is on a sphere? Instructor: Pesses Points north Crucial to human development Longitude & Latitude An imaginary grid that covers the surface of the Earth 4

5 DMS Reported in Degrees, Minutes, Seconds (DMS) & the direction. ô 360 (degrees) around a sphere ô 60 (minutes) in a degree ó 1/60 ô 60 (seconds) in a minute (though we won t use these in this class ) Lines of Latitude Also called parallels Gives us North and South coordinates Lines run from East to West ô Example: N Lines of Latitude Latitude is the measured angle north or south of the Equator Finding Your Latitude Finding Your Latitude Angle measured between the horizon & solar noon Corrected with celestial charts & the analemma We can use other stars too Polaris ô The North Star directly over the North Pole ô Use the Southern Cross in the Southern Hemisphere Instructor: Pesses 5

6 Finding Your Latitude Lines of Longitude Measure the angle between Polaris & the horizon to find your latitude The Earth rotates on its axis; we use this to map out longitude. Lines of Longitude Lines of Longitude Meridians Great circles ô The shortest route between 2 points on a sphere. Origin Point Origin Point The Prime Meridian runs through Greenwich, England Given the numerical value of 0. Other meridians numbered in degrees, to the east & the west from Greenwich. ô The direction is important Instructor: Pesses 6

7 Finding Longitude It s one thing to look up longitude on a globe, but what about finding it on a ship in the ocean? Finding Longitude Determined by measuring the difference between the time at the prime meridian & solar noon at the meridian in question Rotation Rotation The sun moves through the sky every 24 hours, travels 360 (360/24 = 15 per hour) Earth rotates to the East If your time is later than Greenwich s, you have travelled East If earlier, travelled West Finding Longitude Finding Longitude So 3pm in Greenwich & noon at your location means you are at 45 West So 3pm in Greenwich & noon at your location means you are at 45 West ô 3 hours x 15 degrees = 45 degrees traveled Instructor: Pesses 7

8 Finding Longitude Harrison s Chronometer So 3pm in Greenwich & noon at your location means you are at 45 West ô 3 hours x 15 degrees = 45 degrees traveled But can you see the problem with this technique? The Graticule Coordinate System This system of latitude and longitude is referred to as the graticule Parallels & meridians cross at right angles (90 ) A grid used to organize a map or globe for the purposes of determining location and/or distance. GPS PLSS Global Positioning System (G.P.S.) Has made finding your location much easier Public Land Survey System (P.L.S.S.) ô Developed by Thomas Jefferson to facilitate westward expansion of the US ô Often referred to as Township and Range Instructor: Pesses 8

9 GEOG 101 8/16/16 Baselines & Meridians These give your origin point ô ô ô 6 mile grids are built off of the meridian and base line Townships (or Tiers) are counted north-south Range are counted east-west Sections Each township and range square is divided into 36 sections. Each section is therefore 1 square mile or 640 acres Influence on the Landscape Best seen from the air Instructor: Pesses Other land divisions French long lots in Louisiana 9

10 Next Time How maps work ô Projections ô Scale Instructor: Pesses 10