CIRCUMFERENCE OF THE EARTH

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Presentation transcript:

CIRCUMFERENCE OF THE EARTH

In the third century BC, the Greek mathematician Eratosthenes was asked to find the circumference of the earth.

He knew that the rays of the sun fall to earth in parallel lines.

He knew that when parallel lines are cut by a transversal alternate interior angles have the same measure

He knew that if he went to the city of syene at noon on June 19

He knew that if he went to the city of syene at noon on June 19 he would see light shining out of the famous well.

WELCOME TO SYENE HOME OF FAMOUS WELL

The sunlight reflects only if the sun is directly overhead!

The rays of the sun are perpendicular to the earth at this point

I know the distance between Syene and Alexandia. On June 19 I will be in Alexandria. There I will erect a flagpole

flagpole at Alexandria well at Syene

The measure of this angle is 1/50 of a circle

1/50 of a circle 1/50 of a circle

Fifty times the distance between Syene and Alexandia is the circumference of the earth!

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