Chapter 1 - The Measure of the Earth

Shape and Size of the Earth

Aristotle (4th century B.C.) knew the Earth was spherical

(Earth casts circular shadow on moon during eclipses)

Eratosthenes (247 B.C.) determined the approximate size of the Earth (~25,000 mi around)

(difference in angle of sun at Alexandria and Syene Egypt)

Newton Reasoned Earth's shape should be a slightly flattened sphere (Earth as Geoid)

(centrifugal force on spinning Earth should cause equatorial bulge)

modern measurements confirm all

Location and Time

Ptolemy (1st & 2nd century A.D.) divided circle into 360°

Latitude

lines of latitude (parallels) run E-W, measure distance N & S of equator

latitudes are angular distances from 0° (equator) to 90° (poles)

can determine using elevation of sun, Polaris, and Southern Cross on known date

Longitude

lines of longitude (meridians) run N-S, measure distance E & W of Prime Meridian

longitudes are angular distances from 0°(Greenwich) to 180° E or W

can determine using direction to sun or stars, local time, and Greenwhich time

Great Circles and Small Circles

great circles are the largest circles that can be drawn on a given sphere

small circles are any other circle

longitude meridians are great circles

latitude parallels are small circles (all except equator which is a great circle)

the shortest distance between two points is on a great circle connecting them

Prime Meridian

the longitude of the Royal Observatory at Greenwich, Engl. chosen as 0° longitude

Standard Time

there are 360° of longitude around the Earth

the Earth takes 24 hours to go around once (sunrise to sunrise)

the Earth is subdivided into 24 time zones that are each 15° wide (360 / 24 = 15)

International Date Line

180° longitude is called the international date line (but modified for practical reasons)

calendar days begin at the International Date Line

to the east of the date line, the date is one day earlier than the date to the west

Map Scales and Projections

Map Scales

tell how great the distances depicted on a map are in the real world

graphical scales show a bar or line that is labeled with the real distance represented

verbal scales: e.g., "1 inch equals 4.5 miles" [1 in on map represents 4.5 mi real world]

ratio scale: e.g., "1:24,000" [real world distances are 24,000 times map distance]

Map Projections

round globes accurately depict the Earth

flat maps distort the Earth

equal area maps maintain proper land mass sizes but distort directions and shapes

true shape (equal angle) maps preserve directions but distort size & distance)