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The Mirror Maker Who Waits for Glass to Cool

6th grade nonfiction passage about telescope mirror maker: 237 words, six questions, an answer key and vocabulary.

6th grade nonfiction telescope mirror maker 237 words

The Mirror Maker Who Waits for Glass to Cool

Many large telescopes gather light with a mirror shaped like a shallow bowl. The mirror must be extremely smooth. Its surface can be off by only a tiny fraction of the width of a light wave, which is far thinner than a human hair. Making a surface that perfect is the work of an optician, and it takes patience as much as skill.

The job begins with a thick disk of glass. The optician grinds it against another disk, using wet gritty powder between them. The grinding wears the glass into a gentle curve. As the work goes on, the optician switches to finer and finer powders, and each stage removes the scratches left by the stage before.

Polishing comes next, and it brings the surface to a shine. At every step, the optician stops to test the mirror by shining a light on it and studying the reflection. If a spot is too high or too low, the next round of work is aimed right at that spot.

There is a catch. Glass changes shape when it warms up, even a little. A person's hands or a warm room can make the mirror swell for a moment and give a false test. So the optician waits for the glass to settle to room temperature before trusting a measurement. A mirror can take weeks or months to finish, and a single hurried step can undo the progress.

Questions

  1. What shape does a telescope mirror have? in the text

  2. What does the optician use between the two glass disks when grinding? in the text

  3. Why does the optician switch to finer powders? in the text

  4. How does the optician test the mirror? in the text

  5. Why must the optician wait for the glass to reach room temperature? think about it

  6. Why does the passage say patience matters as much as skill? think about it

Words to know

optician
a person who makes lenses and mirrors
grinds
rubs hard against something to wear it down
gritty
full of tiny rough bits like sand
polishing
rubbing a surface until it is smooth and shiny
swell
to grow a little larger
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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 · 230 words · Flesch-Kincaid grade 3.6

Many big telescopes gather light with a mirror shaped like a shallow bowl. The mirror must be very smooth. Its surface can be off by only a tiny bit of the width of a light wave. That is much thinner than a hair. Making a surface this perfect is the work of an optician. It takes patience as much as skill.

The job starts with a thick disk of glass. The optician grinds it against another disk. Wet gritty powder goes between them. The grinding wears the glass into a gentle curve. Then the optician uses finer and finer powders. Each stage takes away the scratches from the stage before.

Next comes polishing. It makes the surface shine. At each step, the optician stops to test the mirror. A light is shone on it, and the optician studies the reflection. If a spot is too high or too low, the next round of work goes right to that spot.

But there is a catch. Glass changes shape when it gets warm, even a little. A person's hands or a warm room can make the mirror swell for a while. That gives a false test. So the optician waits for the glass to cool to room temperature. Only then does the optician trust the test. A mirror can take weeks or months to finish. One hurried step can undo the work.

▲ This passage · 237 words · Flesch-Kincaid grade 6.2

Many large telescopes gather light with a mirror shaped like a shallow bowl. The mirror must be extremely smooth. Its surface can be off by only a tiny fraction of the width of a light wave, which is far thinner than a human hair. Making a surface that perfect is the work of an optician, and it takes patience as much as skill.

The job begins with a thick disk of glass. The optician grinds it against another disk, using wet gritty powder between them. The grinding wears the glass into a gentle curve. As the work goes on, the optician switches to finer and finer powders, and each stage removes the scratches left by the stage before.

Polishing comes next, and it brings the surface to a shine. At every step, the optician stops to test the mirror by shining a light on it and studying the reflection. If a spot is too high or too low, the next round of work is aimed right at that spot.

There is a catch. Glass changes shape when it warms up, even a little. A person's hands or a warm room can make the mirror swell for a moment and give a false test. So the optician waits for the glass to settle to room temperature before trusting a measurement. A mirror can take weeks or months to finish, and a single hurried step can undo the progress.

■ Harder · 247 words · Flesch-Kincaid grade 8.7

Many large telescopes collect light with a mirror that is shaped like a shallow bowl. The mirror must be extraordinarily smooth: its surface can deviate by only a tiny fraction of the width of a light wave, which is far thinner than a human hair. Producing a surface that flawless is the work of an optician, and it demands patience just as much as skill.

The job begins with a thick disk of glass. The optician grinds it against a second disk, using wet gritty powder between the two. The grinding gradually wears the glass into a gentle curve. As the work progresses, the optician switches to progressively finer powders, and each stage erases the scratches left behind by the stage before it.

Polishing follows, and it brings the surface to a brilliant shine. At every step, the optician pauses to test the mirror by directing a light onto it and carefully studying the reflection. If a spot is too high or too low, the next round of work is concentrated precisely on that spot.

There is, however, an unexpected complication. Glass changes shape when it warms up, even slightly. A person's hands or a warm room can cause the mirror to swell for a time and produce a misleading test. Therefore the optician waits for the glass to settle to room temperature before trusting any measurement. A mirror may take weeks or even months to complete, and a single hurried step can undo all the progress.

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 optician, grinds, gritty, polishing and swell 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 5 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 "The Mirror Maker Who Waits for Glass to Cool"?

It was written for 6th grade. It has 237 words and works out to a Flesch-Kincaid grade level of about 6.2. 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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