No matter what kind of map is made, some portion of the Earth’s surface will always look either too small, too big, or out of place. Mapmakers have, however, found ways to limit the distortion of shape, size, distance and direction.

How do we know the Earth is not flat? EVIDENCE FOR EARTH’S SPHERICAL SHAPE –Ships appear to “sink” as they approach the horizon –Other celestial objects are round. –Now we can see earth from space, and photograph it! BUT, the most important proof that Earth is round is the fact that the altitude of Polaris increases as you move toward the North pole, or decreases as you move toward the equator! – This would not happen on a flat Earth. A quicker way to say it is “the altitude of Polaris changes directly with latitude.”

This is a more realistic view of Earth It’s not really as “oblate” or oval But it’s still an oblate sphere – can you tell by looking at the dimensions?

Rough or Smooth? This picture from space makes Earth look very smooth. This picture of the Grand Canyon makes the Earth look rough Which is the case?

Rough Vs. Smooth: Its all relative! When standing on Earth looking at the Grand Canyon the Earth’s surface looks very rough. –This is because you are comparing the surface with yourself as a frame of reference (a scale to compare size) When seen from space, the Earth looks very smooth. –This is because you are comparing the mountains and valleys with the entire planet for scale!

MEASURING EARTH How would you measure the circumference of Earth? Could you determine it using no technology? It’s not a very simple problem. A Greek scientist named Eratosthenes used a simple solution to determine earth's circumference – 2,200 years ago!

Proportions! A proportion is making the mathematical statement that two ratios are equal Eratosthenes knew if he could figure out any portion of the 360 circumference of the Earth he could solve for the whole circumference! Remarkably, Eratosthenes determined the circumference to be 25,000 miles, just 99 miles over the actual circumference at the equator (24,901 miles). %D =. 396%! What was his percent error?

Where are we? How would you keep track of where you are on such a big planet? At first, people used stars…

USING STARS TO NAVIGATE Early sailors used a device like this to know where they were on this huge Earth. The device was used to measure the angle between a star, and the horizon. This angle is the altitude of the star.

The Altitude of Polaris By far the most important star was Polaris, or the North star, because the altitude of Polaris told you how far North of the equator you were (latitude!) Remember as distance increases the altitude decreases or angular distance from the horizon! But how to find Polaris? –Contrary to popular belief Polaris is NOT the brightest star in the northern hemisphere sky, in fact it barely makes the top 50!!

Finding Polaris! Much more important then Finding Nemo! Polaris is also called the North Star, or the Load Star. Just look for the Big Dipper -- and notice that the Dipper has a bowl and a handle. Draw a line between the two outermost stars in the bowl of the Big Dipper. This line points to Polaris, the North Star!

Additionally: Most stars rise and set -- just like the sun and moon. But Polaris is like the hub of a wheel -- it stays put in the northern sky, while all the other stars appear to circle around it (in fact we are spinning on our axis and Polaris is centered above our axis!)

Dividing up Earth’s Surface Latitude is distance north or south of the equator, measured in degrees. Longitude is distance east or west of the prime meridian, measured in degrees. Latitude and Longitude are lines on the globe that are used to determine location.

Latitude is: The Angular distance north or south of the equator Parallel lines, equator is zero degrees, north pole is 90 degrees north EQUAL TO ALTITUDE OF POLARIS!!!

LONGITUDE AND TIME Since longitude is determined by taking the time of solar noon (sun at maximum altitude in the sky for the day) at your location and comparing it to solar noon at the prime meridian. It is known that the Earth makes one complete rotation about its axis every 24 hours. 360 degrees divided by 24hrs calculates to 15 degrees/hr.

Greenwich Time! If you know time at one location, you can say that it is one hour earlier for every 15 degrees to the west. Another way : The occurrence of any time moves west at 15 degrees per hour. So when you measure your solar noon if it is 2:00 PM in Greenwich (on prime meridian) you know you are 30 degrees west of Greenwich!

LONGITUDE IS…. Angular distance east or west of the prime meridian Longitude lines are not parallel, and get closer together as you move towards the poles NOT determined by the location of Polaris, but another star – THE SUN!

Longitude lines run up and down (North & South) and determine your location east or west of the prime meridian Latitude lines run east/west and determine your location north, or south of the equator