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Minutes from ME

Span the Globe


As school begins to wind down that persistent question "What do we do after this?" takes on new significance. Its answer is no longer "Gym period" or "Art" or "Science;" the reply in June is "Vacation!"

We talk about our summer plans ... the places we'll go, the people we'll see. Seeing a chance to use some comparative adjectives we begin to wonder. Will the destinations be hotter or colder than here? Wetter or drier? Higher or lower? Bigger or smaller? Contrasting which vacation spots are farther or nearer brings up interestingly complex travel arrangements which send us to consult a globe. Does a suggested airline route from Philadelphia to Anchorage, Alaska, which goes by way of Houston and Seattle, make any sense? We check the globe and still cannot understand that trip but that IS the way we'll get to Anchorage! Seeing the globe gives us more ideas, we wonder who will be traveling northernmost, or southernmost or the two other compass directions. There is a way of describing locations very accurately so that we can compare their positions on the earth's surface, it's LATITUDE and LONGITUDE.

Globe Bar

Over two thousand years ago Ptolemy of Alexandria, with a mathematician's instinct to define and measure, introduced the idea of latitude and longitude to measure the surface of the Earth he believed to be spherical; two hundred years or so earlier Eratosthanes had deduced the Earth's circumference quite accurately by noting the angular difference of the sun between Syene and Alexandria and the linear distance between the two cities. Yet we are told that fifteen hundred years later contemporaries of Christopher Columbus still believed the Earth to be flat - Go Figure!

The surface of our spherical Earth is divided by a lattice of imaginary lines:

The Equator is a great circle around the earth's middle, exactly half way between the North Pole and the South Pole. Lines of Latitude go around the earth parallel to the equator to the north and south of it. With the equator being zero the values of latitude can be up to 90 degrees either north or south.

Lines of Longitude go around the earth passing through the North and South Poles and through Greenwich, England, the place where the standard reference meridian of zero was set up. With this Greenwich Meridian being zero, the values of longitude can be up to 180 degrees to the east or west of it.

Latitude and longitude are measured in angular units, degrees, which relate to the "roundness" of the earth and describe an arc at its surface. (For our purposes we disregard the finer subdivisions of degrees into minutes and seconds).

Recent measurements of the earth show it to be 24,902 miles around at the equator and 24, 818 miles around through the north and south poles (remember the earth is "flattened" at the poles). Dividing the circumference of the earth by the 360 degrees in each case, the distance on the earth's surface for each imaginary one degree of latitude or longitude is approximately 70 miles.

Globe Bar


With a globe in one hand and a computer mouse in the other, we set out to investigate latitude and longitude. Comparison of places on a globe provides answers where differences are obviously large but often, as can be seen in our examples below, we need precise measurements to be finally sure. For this project we use the How Far Is It? web site which gives precise location (in latitude and longitude) of our starting place and our destination, as well as the distance between the two. This site links to the PARC Map Server which gives a great opportunity to "zoom in" to a close look at the destination's locale from a point high above the earth.


We make a table listing some of our journeys' ends and enter the latitude and longitude values, found through How Far Is It?, for each. Bar charts ("math pictures") make the data easier to understand, so we also prepare the charts shown here.


Latitudes bar chart

Longitudes bar chart

Comparing our charts to the globe we see, for instance, that Jordan, after going a long way south, ends up in a place farther EAST of us, and Dick in Sydney is only about 70 miles (one degree) farther from the South Pole than Jordan on the other side of the world.

Now for some questions:
Who went farthest in each direction?
Who stayed closest to home?
Who stayed closest to the Equator?
Who stayed closest to the Greenwich Meridian?


Students gather in pairs and invent or answer such questions as:
1. 52 North: 21 East, the capital of Poland.
2. 35 North: 139 East, Mount Fuji is nearby.
3. 45 North: 18E East, Swedish spoken here.
4. 40 North: 74 West, Statue of Liberty site.
5. 60 South: 60 West, penguin heaven!

Globe Bar

Finally, to see how your vacation destination looks from space and check on current conditions go to Earth and Moon Viewer and zoom in on your spot as it is pictured by satellite right now; see if it's day or night there now.

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