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# Observations and Experiments

## Observations and experiments are used to test hypotheses.

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Practice Observations and Experiments

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Earth Was Never Flat!

### Earth Was Never Flat!

Credit: NASA
Source: http://commons.wikimedia.org/wiki/File:Nasa_blue_marble.jpg

We know Earth is round because astronauts see it from space. But humans first went into space a little more than 50 years ago. How did people know the Earth was round before that?

#### How Did they Know the World is Round?

The Ancient Greeks lived millennia before the first telescopes. Their world did not extend far beyond the Mediterranean region. But learned Greeks knew that the Earth was round. Ancient Romans followed their lead. How did they know the world was round? Why did people lose that knowledge and how did they get it back?

Source: http://en.wikipedia.org/wiki/File:Flat_earth.png

Flat Earth model - white surrounding was thought to be a wall of ice so people don't fall off Earth [Figure2]

#### Ten Ways to Know

With the link below, learn how people knew the Earth was round. Then answer the following questions.

1. List the three reasons that the Ancient Greeks could have known the Earth was round.
2. There is one additional reason that the explorers around the time of Magellan could have known that the Earth was round.
3. Galileo invented the telescope several decades after Magellan’s voyage. How was the telescope used to determine the shape of the Earth?
4. As Europeans spread across the globe, including into the Southern Hemisphere, they made many observations. What are additional reasons that they could have known Earth was round?
5. The final reason is more of a thought experiment since no one could travel 30,000 miles without running into water. What could you use as a model to test this reason that Earth is round?

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