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Two Shadows Helped Measure the Whole Earth

6th grade nonfiction passage about measuring earth with shadows: 237 words, six questions, an answer key and vocabulary.

6th grade nonfiction measuring earth with shadows 237 words

Two Shadows Helped Measure the Whole Earth

More than two thousand years ago, a Greek scholar named Eratosthenes worked in the great library in Alexandria, in Egypt. He heard about a deep well in a southern town called Syene. On one day each summer, at noon, sunlight shone straight down the well and lit the water at the bottom. This meant that the sun was directly overhead in Syene at that moment.

Eratosthenes wondered about the same day in Alexandria. He set up a tall pole and watched its shadow at noon. The pole did cast a shadow, which meant the sun was not straight overhead there. He measured how far the sun's rays tilted from the pole, and it was about one fiftieth of a full circle.

Here is the clever part. Sunlight reaches Earth in nearly parallel rays. If the ground were flat, the two towns would have the same shadows. Different shadows meant the surface curved between them. The angle of the shadow matched the curve of Earth between the two places.

Eratosthenes knew roughly how far apart the towns were, because surveyors had paced it off. If that distance was one fiftieth of the way around Earth, then the whole trip had to be fifty times longer. He multiplied, and he got a number for the size of the planet.

His answer was surprisingly close to what we know today. He used only a pole, the sun and good thinking.

Questions

  1. What happened in the well at Syene at noon on one summer day? in the text

  2. What did the pole in Alexandria show? in the text

  3. What fraction of a full circle was the angle of the shadow? in the text

  4. Why did different shadows in the two towns suggest that Earth is curved? think about it

  5. How did Eratosthenes get the size of the whole Earth from the distance between the towns? think about it

  6. What tools did Eratosthenes use? in the text

Words to know

scholar
a person who studies and knows a lot
overhead
directly above you
parallel
lines going the same way that never meet
surveyors
people who measure land and distances
curved
bent in a smooth round shape
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One passage, three levels

The same topic and facts written three ways, so a mixed class can read and talk about one text. Each group’s sheet shows only a shape; the key says which is which.

● Easier · 229 words · Flesch-Kincaid grade 3.5

More than two thousand years ago, a Greek scholar named Eratosthenes worked in a great library in Alexandria, in Egypt. He heard about a deep well in a southern town called Syene. On one day each summer, at noon, the sun shone straight down the well. It lit the water at the bottom. That meant the sun was right overhead in Syene.

Eratosthenes wondered about the same day in Alexandria. He set up a tall pole. He watched its shadow at noon. The pole did cast a shadow. So the sun was not straight overhead there. He measured how far the sun's rays tilted from the pole. It was about one fiftieth of a full circle.

Here is the clever part. Sunlight reaches Earth in nearly parallel rays. If the ground were flat, both towns would have the same shadows. They did not. So the ground must curve between them. The angle of the shadow matched the curve of Earth between the two places.

Eratosthenes knew about how far apart the towns were. Surveyors had paced it off. That distance was one fiftieth of the way around Earth. So the whole trip had to be fifty times longer. He multiplied. He got a number for the size of the planet.

His answer was close to what we know today. He only used a pole, the sun and good thinking.

▲ This passage · 237 words · Flesch-Kincaid grade 5.7

More than two thousand years ago, a Greek scholar named Eratosthenes worked in the great library in Alexandria, in Egypt. He heard about a deep well in a southern town called Syene. On one day each summer, at noon, sunlight shone straight down the well and lit the water at the bottom. This meant that the sun was directly overhead in Syene at that moment.

Eratosthenes wondered about the same day in Alexandria. He set up a tall pole and watched its shadow at noon. The pole did cast a shadow, which meant the sun was not straight overhead there. He measured how far the sun's rays tilted from the pole, and it was about one fiftieth of a full circle.

Here is the clever part. Sunlight reaches Earth in nearly parallel rays. If the ground were flat, the two towns would have the same shadows. Different shadows meant the surface curved between them. The angle of the shadow matched the curve of Earth between the two places.

Eratosthenes knew roughly how far apart the towns were, because surveyors had paced it off. If that distance was one fiftieth of the way around Earth, then the whole trip had to be fifty times longer. He multiplied, and he got a number for the size of the planet.

His answer was surprisingly close to what we know today. He used only a pole, the sun and good thinking.

■ Harder · 255 words · Flesch-Kincaid grade 7.9

More than two thousand years ago, a Greek scholar named Eratosthenes worked in the renowned library at Alexandria, in Egypt. He learned of a deep well in a southern town called Syene. On one particular day each summer, at noon, sunlight shone straight down the well and illuminated the water at the bottom. This indicated that the sun was directly overhead in Syene at that moment.

Eratosthenes became curious about the same day in Alexandria. He erected a tall pole and observed its shadow at noon. The pole did cast a shadow, which meant the sun was not straight overhead there. He measured how far the sun's rays were slanted away from the pole, and the angle turned out to be about one fiftieth of a full circle.

Here is the clever part. Sunlight reaches Earth in nearly parallel rays. If the ground were flat, the two towns would have identical shadows. Because the shadows differed, the surface had to curve between them, and the angle of the shadow matched the curve of Earth between the two places.

Eratosthenes knew approximately how far apart the towns were, since surveyors had paced off the distance. If that distance represented one fiftieth of the way around Earth, then the complete journey had to be fifty times longer. He multiplied, and he arrived at a figure for the size of the entire planet.

His answer was surprisingly close to what we know today, and he reached it using nothing more than a pole, the sun and careful thinking.

Download as one PDF

How to use it

  1. Press Read it big (or B) to put the text on the projector, or Full screen (F) to fill the whole screen.
  2. Ask the questions one at a time and use Show answer when the class has decided. A shows or hides every answer.
  3. Print student copy for the class, or Print with answers for yourself.

Ideas for class

  • Before reading, put scholar, overhead, parallel, surveyors and curved on the board with their meanings from the Words to know section and have students predict what the text will be about.
  • Read it aloud once while students follow along, then have them reread it alone or with a partner. At a calm 100 words a minute it takes about 2 minutes to read aloud.
  • Use the Read it big button (or B) to put the text on the projector, and Show answer on one question at a time so the class commits to an answer first.
  • Question 4 asks the reader to infer. Ask students to point to the words in the passage that led them to their answer.
  • Ask students to write one question the passage did not answer, then look for the answer in a book or on a classroom screen.
  • Print the student copy for independent work and keep the answer-key copy for yourself.

Related

Questions

What reading level is "Two Shadows Helped Measure the Whole Earth"?

It was written for 6th grade. It has 237 words and works out to a Flesch-Kincaid grade level of about 5.7. That is a formula's estimate from sentence length and syllables, and it is not a Lexile or a guided reading level, so check it against your students.

What do the questions ask?

There are six. 4 ask for something the text says directly and 2 ask the reader to work something out from clues. Each has an answer in the key, and the answers are written as a teacher would accept them, not as the only possible wording.

How long does it take to read?

About 2 minutes read aloud at 100 words a minute. For a one-minute fluency check, paste it into the fluency timer and use the word count.

Can I print it?

Yes. Print student copy gives the passage, the questions with lines to write on, and the word meanings. Print with answers gives the same page with the answers filled in. Both are made in your browser.

Is this passage from a published book?

No. It was written for Peabody Teach, so there is no book to buy and no login to read it.

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