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2.1: Earth's Shape

Difficulty Level: Basic Created by: CK-12
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What is a flat-earther?

Flat-earther is a term used to describe someone who believes something despite the evidence. Or who does not believe something despite the evidence. There are actually people who believe that Earth is flat. They say that satellite photos are faked. They believe that the Apollo moon landings were faked. But there are very few people who actually believe that Earth is flat around today. There are, however, plenty of people who can be called flat-earthers. These people believe (or disbelieve) something despite the evidence.

Earth’s Shape

As you walk around, the ground looks flat. So why do you think that Earth is round? The best reason is that we have pictures of Earth taken from space. These photos show that Earth is round. Astronauts aboard the Apollo 17 shuttle took this one, called “The Blue Marble” ( Figure below ). Earth looks like a giant blue and white ball.

This is how the Earth looks from space - like a blue and white marble.

Did people only come to think that Earth is round when spacecraft took photos? No! Even the ancient Greeks knew that Earth was round. They figured this out by observing the arc shape of the shadow on the Moon during a lunar eclipse. Since Galileo, people can look through a telescope and see that the planets orbit around the Sun. These bodies - the Sun and each of the planets - are round. If Earth is a planet, it is certainly round.

Another way to tell Earth's is round is to look at ships sailing off into the distance. What do you see when you watch a tall ship sail over the horizon of the Earth? The bottom part of the ship disappears faster than the top part ( Figure below ). What would that ship look like if Earth was flat? No part of it would disappear before the other. It would all just get smaller as it moved further away.

Earth’s curvature is noticeable when objects at a distance are below the arc.

Hemispheres

Earth is a sphere (technically, an oblate spheroid, a bit squashed at the poles). As a sphere, it can be divided. Half of a sphere is a hemisphere . Earth is divided into hemispheres: north, south, east, west (see Figure below ).

Remember that the Equator is the line that falls at 0 o . North of the equator is the northern hemisphere . South of the equator is the southern hemisphere . The North Pole is at 90 o N. So there are 90 degree lines in the Northern Hemisphere. The South Pole is 90 o S. So there are 90 degree lines in the Southern Hemisphere.

Earth also has an eastern hemisphere and a western hemisphere . They are just made by humans so that locations can more easily be specified. The Prime Meridian is 0 o longitude and passes through Greenwich, England. The International Date Line is the 180 o meridian. The eastern hemisphere is east of the Prime Meridian to the International Date Line. It includes eastern Europe and Asia. The western hemisphere west of the Primer Meridian to the International Date Line. It includes western Europe and the Americas.

Summary

  • Ancient Greeks knew that Earth was round. They saw the shadow the planet cast on the Moon during a lunar eclipse.
  • Through a simple telescope the other planets appear to be round. So Earth must be round.
  • A boat does not get smaller with distance but sinks below the horizon. This is more evidence that Earth is round.

Interactive Practice

Use this resource to answer the questions that follow.

  1. What was the first photo of Earth? What did it prove?
  2. Why are bodies in space round?
  3. How did the planets form?
  4. What is the only shape in nature that looks the same from all directions?
  5. Why are there odd-shaped objects in space?

Review

  1. Before telescopes and spaceships, how did people know that Earth is round?
  2. What a ship sailing away from you look like if Earth was flat? If Earth was round?
  3. Define where the hemispheres are located: northern, southern, western and eastern.

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Difficulty Level:

Basic

Grades:

6 , 7

Date Created:

Jan 04, 2013

Last Modified:

Jun 16, 2014
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