Telescope Girl

Resource for Grades K-8

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Media Type:
Video

Running Time: 3m 24s
Size: 8.6 MB

Source: ZOOM

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This video segment from ZOOM features a young telescope enthusiast and her reflecting telescope. She explains how this type of telescope works and shows you what you can see through it. She also demonstrates how you can make a reflecting telescope like hers using relatively common and inexpensive materials.

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Background Essay

In a reflecting telescope, a mirror gathers light at the base of a tube and reflects it back to a point of focus near the open end of the tube. There, a second, smaller mirror -- flat and angled -- reflects light to an eyepiece on the side of the tube. Looking through the eyepiece, the observer sees an image, which has been made larger, or magnified, so that even an object at a great distance appears as if nearby.

Mirrors and lenses perform the same basic task in telescopes -- they collect light and then direct it to a point of focus. However, telescopes that use mirrors have certain advantages over those with lenses. To begin with, it is easier to produce a high-quality mirror than a high-quality lens. A mirror requires only one good surface, but a lens requires good glass all the way through because light must pass completely through it without being absorbed or scattered. Also, light passing through a lens separates into its many different wavelengths, which may cause the color of observed objects to be distorted, especially around the edges. Mirrors do not separate light in this way, so light waves of all wavelengths behave the same way when reflected.

The first step in preparing a mirror for use in a reflecting telescope is to grind, shape, and smooth a rough glass -- called a blank -- with either a specialized grinding tool or a second mirror blank and some abrasive grit. The stroking action involved in rotating the glass and the tool or second blank in opposite directions and at random angles causes the entire surface of the mirror to become curved. Once it is ground and shaped, the mirror glass is ready for polishing. Polishing leaves the glass with a smooth, inward-curving, spherical surface, which is coated with a thin layer of aluminum to make it reflective. The mirror will then reflect incoming light rays and, because of its shape, focus them in a single point.

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Discussion Questions

How does Katy's reflecting telescope work?

What materials did Katy use to make her telescope?

Have you ever looked through a telescope? If so, how easy was it to see the object in the sky?

How do telescopes help us understand the universe?

What other things could be used to look at the moon and stars? How effective would they be?

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Transcript

(knocking)(hinge squeaks)

KATY HOAGLAND: Did you ever wonder if there's life on other planets? How the galaxies formed? Or if a human will ever walk on Pluto? Hi, my name is Katy Hoagland. I'm 12 years old and I live in Sherman Oaks, California. When I grow up, I want to be an astrophysicist, which is a person who studies the stars and planets spinning through space. There are countless objects to study in the sky.

I agree with many astronomers who think that there are more stars in our universe than there are grains of sand on this beach, possibly more stars than there are grains of sand on every beach in the entire world. But most of the objects in space are too far away to see very well your naked eye. That's why you need a telescope.

This is my telescope. I built it myself. It magnifies faraway objects and makes them appear bigger, like the Moon. My telescope took me 30 hours to build. It's mostly made of ordinary materials. The design is so simple that anyone can build it. It's lightweight and I can move it around myself.

The tube is made of cardboard. (knocks) (knocking) The base is plywood. This shower cap works as a dust cover to keep the dust off the mirror. It's a ten-inch reflecting telescope and this is how it works. Light from stars and planets enters the top of the telescope and is collected at the bottom of the tube by a ten-inch curved mirror.

The light then bounces off the ten-inch mirror back up the tube to the second smaller mirror here. The light is then reflected into the eyepiece, which magnifies, or enlarges, the image.

The hardest part is grinding the glass for the mirror. It takes about ten hours. After we're done with that, we take it to an aluminizer, who makes it more like a mirror. This is the finished product, a ten-inch reflector.

Is there life out there? Can we colonize other planets? We don't know the answers to all of these questions yet, so for now, I'll just keep on stargazing. Hey, maybe there's another kid with a telescope at the other end of the Milky Way looking out at me.