1. Earth’s Grid System
The Earth is a near perfect sphere (oblate spheroid) and for centuries mankind has attempted and succeeded in producing a grid system to represent the earth’s surface.
Imaginary lines that divide the Earth
Drawn east /west and north/south
Called meridians
These lines are sometimes referred to as parallels.

2. Earth’s Grid System – Historical Perspective
History:
Positioned themselves according to landmarks and surface features
2,500 years ago civilizations used crude measurements of the horizon in relation to the stars in order to plot coordinates (vague). Using these techniques, a person latitude could be formulated, however to be more exact longitude is required.
Calculating longitude has been a difficult ‘nut to crack’ since the time of Hipparchus 190BC, whereby the measurement of lunar eclipses and prime meridian was suggested. However without the use of an accurate clock (which wasn’t invented until 1656 with the pendulum clock).
Cassini = used lunar eclipses to calculate longitude on an island in the Caribbean and compared the time in France to formulate longitude.
Calculating longitude whilst at sea was a more complex issue to calculate
Time is the KEY – 360 degrees – rotation of Earth around the axis – 24 hours clock (length of day)
360/24 = 15 – therefore every 1 hour difference in midday sun is 15 degree in longitude on the Earth’s surface
It works out to be 4 mins per 1 degree of longitude
Comparison of time between two locations (Greenwich, London vs. current location) either east or west.

3. Earth’s Grid System – Latitude
Lines of latitude are numbered from 0° at the equator to 90° N. at the North Pole.
Latitude is defined as a measurement of distance in degrees north and south of the equator
North Pole [ ]
Lines of latitude are numbered from 0° at the equator to 90° S. at the South Pole.
There are 90 degrees of latitude from the equator to each of the poles, north and south.
Latitude lines are parallel, that is they are the same distance apart
South Pole

4. Earth’s Grid System – Equator
The equator is the longest of all lines of latitude
It divides the earth in half and is measured as 0° (Zero degrees).
Length - 24,874 miles (40,030 km)
Roughly 14 miles longer around than tall!

5. Earth’s Grid System – Longitude

6. Earth’s Grid System – Prime Meridian
The Prime Meridian (0°) and the 180° line split the earth into the Western Hemisphere and Eastern Hemisphere.
Western Hemisphere
Eastern Hemisphere

7. Earth’s Grid System – Time Zones

8. Earth’s Grid System – Time zones and time travel
When we discuss time zones we ALWAYS refer to lines or meridians of LONGITUDE.
Stretching around the earth from east to west
The Earth’s rotation around its axis goes from west to east, therefore the sunlight is moving in a constant and uniform direction. The speed of ‘daylight’ depends on the location (latitude) – how close you are to the poles or equator
Earth spins = 360 degrees
Time for Earth to make a complete 360 spin = 24 hours (1 day)
360/24 = 15 degrees
Therefore every hour the earth rotates on its axis 15 degree to the counter clockwise (right)

9. Earth’s Grid System – Time zones and time travel
Therefore – if you know your time in both locations, you can calculate the longitude.
International date line (IDL) = imaginary line representing the end of one day and the beginning of the next day.
Established in 1884
Located halfway between the prime meridian – 180 degrees
Cross to the west and you GAIN a day – go back to the east and you LOOSE a day or travel BACK IN TIME!!!!

10. Questions and Review:
Ben is heading to Tokyo for his winter break. Ben has a direct flight from Philadelphia leaving at 2PM on Friday and should take 14 hours. His brother, Matt, is joining him and is leaving New York City at 12PM on the same day. His brother’s flight time is expected to be 12 hours but he has a 3 hour layover in Vancouver. Will Ben or Matt land in Tokyo first? What time and day will the later brother arrive?
Answer:
Start – Philly = 2pm afternoon (Friday)
Travelling WEST – to Tokyo
(local time is – 4am the Saturday)
Tokyo 4am + 14 hours = 6pm Saturday
Flight time = 14 hours – 10 hours = 4 difference
Therefore landing in Tokyo at 8am local time
(Saturday) – Ben = 9am = 1 hour difference.

11. Questions and Review: Directions and LONG/LAT coordinates:
How would you express (show) the difference in LAT & LONG between the following locations on the map below:
B to G
D to C
I to J