# The Earth as a Rotating Planet

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The Earth as a Rotating Planet
Chapter 1 The Earth as a Rotating Planet

The Shape of the Earth Earth or Sun moving? Early sailors view……
Is the Earth a perfect sphere? (Quasi-sphere)*—Rotation causes it to bulge at the Equator and flatten at the Poles *Oblate Spheroid

Earth Rotation What is rotation? Why is rotation important?
What direction does the Earth rotate? How long does it take to rotate? 3 main effects of rotation Why is rotation important? Axis serves as reference for geographic grid (latitude and longitude) Measure for time (time zones) Affects physical and life processes

Earth Rotation Figure 1.2 (P. 26)

The Geographic Grid What is a geographic grid?
A system for locating or determining the location of places on the Earth’s surface Demarcations for hemispheres Latitude-Distance N or S of the Equator (0 degrees latitude) **Parallels Tucson is approximately 30 degrees North Longitude-Distance E or W of the Prime Meridian (0 degrees longitude)

A few more points about the latitude and longitude...
Location of a point is given as: latitude (in degrees N or S), longitude (in degrees E or W) There are two techniques for indicating a more detailed location: Decimal degrees: ° Degrees, minutes, seconds: 32° 07’ 48”

Determining a location with latitude and longitude

Parallels and Meridians

Examples What city is located at 37°S and 144°E?
Melbourne, Australia What city is located at 40°N and 105°W? Denver, CO What city is located at 51°N and 0°W? London, England Distances: Given the fact that the circumference of the Earth is 24,860 miles and there are 360° in a circle—How many miles are there in 1 ° of longitude at the Equator?

Calculating Distances between Lines of Latitude
Latitude=(69 miles) x (difference in degrees latitude) Example 1: Calculate the number of miles between Atlanta (33°N, 84°W) and New York City (40°N, 74°W). Latitude=(69) x (7°)=483 miles Example 2: Calculate the number of miles between Prague (50°N, 14°E) and Tripoli, Libya (32°N, 13°E). Latitude=(69) x (18°)=1,242 miles

Calculating Distances between Lines of Longitude (**Difficult)
Longitude=(69 miles) x (COS of parallel traveled) x (difference in degrees long.) Example 1: Calculate the number of miles between Cairo, Egypt (30°N, 31°E) and New Delhi, India (28°N, 77°E). Assume travel along the 29°N parallel. Longitude=(69) x (COS 29) x (46°)=2,777 miles

Map Projections A map is just an abstraction or representation of the real world. The art and science of map-making is called cartography. When you are trying to represent a curved surface on flat paper, you get distortion. Why? Map units

From Earth to a map Start with ellipsoid
Difficult, if not impossible, to take a curved surface and place it on a flat surface Result is distortion All maps have some type of distortion

Five Types of Distortion +1 more
Type Example Shape Circle becomes oval Scale Map scale changes Area Land mass gets bigger Distance Space between cities increases Direction Line varies: N to NW

Polar Projection Characteristics: a circular map centered on North or South Poles and usually showing one hemisphere at most; meridians are straight lines; parallels are circles Advantage: Preserves shapes Disadvantages: scale and area distortion

Mercator Projection A type of conformal projection
Characteristics: rectangular; meridians and parallels are both straight lines Advantage: straight line drawn on map represents a constant compass direction Disadvantages: scale, area, and distance distortion

Goode Projection A type of equal-area projection
Characteristics: odd shape; meridians both straight and curved lines; parallels are straight lines Advantage: Preserves area Disadvantage: shape distortion

Global Time How many world time zones? US? Not exact…why?
Solar noon: period when Sun appears to be highest in the sky Lines of longitude used for time zones 15° of longitude = 1 hr of time (360° in one rotation ÷ 24 hrs = 15° per hour) Example 1: If it is 1 a.m. in Washington D.C., what time is it in Honolulu, Hawaii? 8 p.m Example 2: If it is Noon in Charlotte, NC, what time is it in Madrid, Spain? 6 p.m.

U.S. time zones

Time zones

Global Time (cont’d) International Date Line
Located approximately along 180° Why? 180° ÷ 15° per hr = 12 hr. So if it’s 1pm on the Prime Meridian, the IDL is 1am (next day). West adds a day East subtract a day Daylight Savings Time Midnight Meridian—the meridian that is experiencing midnight (the midnight meridian is NOT stationary)

Time Examples If it is 10 a.m. in Santiago, Chile on Tuesday, May 25, what is the time and date in Taipei, Taiwan? 10 p.m. the same day If it is 1 p.m. in Juneau, Alaska on Saturday, June 12, what is the time and date in Tokyo, Japan? 7 a.m. the next day (June 13)

Longitudnal Time Problems
Example 1: If you depart Washington D.C. (33°N, 77°W) at Noon, at what speed would you have to travel to arrive in Denver, CO (39°N, 105°W) at Noon? Assume travel along the 35°N parallel. Miles=(69) x (COS 35) x (28°)=1,582 miles 1,582 miles / 2 = 791 mph Example 2: If you depart Philadelphia, PA (40°N, 75°W) at 1 p.m., at what speed would you have to travel to arrive in Seattle, WA (48°N, 122°W) at 2 p.m.? Assume travel along the 45°N parallel. Miles=(69) x (COS 45) x (47°)=2,293 miles 2,293 miles / 4 = 573 mph

Earth’s Revolution Movement of the Earth around the Sun
Counterclockwise if viewed from above One revolution = days = 1 yr Responsible for: Seasons Amount of daylight (along with Earth’s tilt)

Earth’s Revolution (cont’d)
When viewed from above, notice that path of Earth is not a perfect circle, but an ellipse or oval. Perihelion: When Earth is closest to the Sun Occurs in January (Northern Hemisphere winter) Aphelion: When Earth is farthest from the Sun Occurs in July (Northern Hemisphere summer)

Earth’s Revolution

Earth’s Revolution (cont’d)
Along with perihelion and aphelion, other times in revolution also have specific names: equinoxes and solstices.

Equinoxes March (vernal) and September (autumnal)
Sun’s rays hit equator at 90° (subsolar pt.) All latitudes receive ~12 hrs of daylight Circle of illumination from North Pole to South Pole

Solstices Occur in June (summer) and December (winter)
Subsolar point in June: Tropic of Cancer (23.5°N); in Dec: Tropic of Capricorn (23.5°S) June solstice: areas from 66.5°N to North Pole receive 24 hrs of daylight (movie – “Insomnia”) Winter solstice: areas from 66.5°S to South Pole receive 24 hrs of daylight

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