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Telescopes and lenses.

Background

Lenses Physics

When we talk about lenses, we need to talk about light. Light is a form of electromagnetic energy made of tiny particles called photons. Light travels in all directions, and always travels away from its source in perfectly straight lines called rays. We see things around us because light rays bounce (or reflect) off objects. The rays pass through our pupils to the retina at the back of the eye. The retina is connected to the eye's optic nerve, which sends information about the image to the brain.

Lenses are transparent pieces of glass or plastic that bend light rays before they reach our eyes. By bending (or refracting) light rays, lenses can change the size, shape, and brightness of objects we see. Lenses must be shaped very carefully and highly polished to work well.

Lenses are made in two basic shapes: convex and concave. A convex lens bulges outward and looks like a dome. A concave lens is shaped like a cave. It bends light so that images look smaller.

Lenses Are Everywhere

We look through lenses every day. There is a lens inside each of our eyes. Sometimes those lenses are imperfect and we wear eyeglasses or contact lenses to correct our vision. Traffic lights and lighthouse lanterns have lenses to spread out light. Cameras and binoculars have lenses, too.

Magnifiers

Magnifiers are convex lenses that we look through to enlarge small print or small objects. The curve of a convex lens spreads out an image so that it takes up a larger portion of your retina and looks bigger. The degree of magnification of a magnifier is expressed as a numeral followed by an X, such as 3X. A 3X magnifier makes an image appear three times larger than your naked eye sees it.

Stamp collectors use magnifiers to see the details of stamps. Botanists use magnifiers to see details of the plants they study. A doctor uses an otoscope, which has a light and a convex lens, to better see inside your ears. Telescopes and microscopes have magnifiers inside.

Refracting Telescopes

Refracting telescopes uses lenses to make faraway objects look closer so we can see them in greater detail. Hans Lippershey, a Dutchman, invented the telescope in 1608. He made a terrestrial telescope, meaning he used it to look at distant things on earth. In 1609, Galileo made the first astronomical telescope, meaning he used it to observe objects in the sky. Galileo discovered craters on the Moon, sunspots on the Sun, and the rings of Saturn. His observations led him to conclude that the Sun, not Earth, was the center of the solar system.

All refracting telescopes are made of a long tube with at least two convex lenses, one at each end of the tube. The objective lens is at the far end of a telescope. It gathers light emitted by stars or reflected off planets or the Moon. In the same way that it is hard to see things in a dimly lit room, it is hard to see dim objects in the sky. The bigger the objective lens is, the more light it can gather and the brighter the object will look.

The objective lens also bends the light rays that pass through it down the tube. The light rays bend inward. The place where they come together (or converge) is the focal point. It is the place where the bright image gathered by the objective lens is sharpest. The distance from the lens to the focal point is the focal length of the lens. Telescopes with a large objective lens must have long tubes because the focal length of the lens is long.

The eyepiece of a refracting telescope is a magnifier. Its job is to enlarge the focused image that arrives at the end of the tube. The eyepiece doesn't have to be large because it only has to magnify the image to the size of a pupil.

The problem with refracting telescopes is that large lenses are heavy. They tend to sag under their own weight and distort images that pass through them. The largest refracting telescope in the world is in Wisconsin. It has an objective lens that is 100 cm (40 inches) wide.

Reflecting Telescopes

In 1668, Isaac Newton invented a new kind of telescope, a reflecting telescope, that uses mirrors instead of lenses to gather and bend light. In reflecting telescopes, the incoming light is gathered by a large, concave mirror, and then reflected by one or more smaller mirrors into your eye. Reflecting telescopes can be much larger than refracting ones because mirrors are thin and relatively lightweight. They have a concave shell behind them to support their weight.

The two largest reflecting telescopes in the world are on the mountain of Mauna Kea in Hawaii. These twin telescopes have mirrors that are 10 meters (11 yards) in diameter. Their surfaces are so big that they could not be made of a single mirror. Instead, they are composed of 36 hexagonal mirrors placed next to each other like tiles on a floor. The Mauna Kea telescopes, however, will be dwarfed by several telescopes now being built. The California Extremely Large Telescope (CELT) will be 30 meters (33 yards) across. Europeans are planning the Overwhelmingly Large (OWL) Telescope whose mirror will be as large as a football field!

Earth-based Telescopes

Optical telescopes are those that gather light. Refracting and reflecting telescopes, as well as catadioptric telescopes that contain both mirrors and lenses, are optical telescopes. Large optical telescopes are housed in buildings called observatories, many of which look like giant igloos with a slit in the roof so the telescope can be pointed at the sky. Because Earth rotates on its axis, an engine slowly moves a large telescope to keep it pointed on a target.

Modern astronomers usually record the data received through a telescope so they can study it later. Telescopes have cameras that take photographs of images. They also have charge-coupled devices (CCDs) that convert light into electronic signals that computers analyze.

The Hubble Telescope

Optical telescopes are usually located on mountaintops to minimize the interference of clouds, dust, city lights, and turbulence in the atmosphere. At high altitudes, the gases of Earth's atmosphere are thinner. To avoid these problems of interference, the U.S. National Aeronautics and Space Administration (NASA) launched the Hubble Space Telescope from the Space Shuttle in 1990. Hubble orbits about 380 miles above Earth. Because it encounters no atmospheric interference, it provides sharper images of astronomical bodies than other telescopes do. It sends data back to Earth by radio.

Hubble has provided us with views of the birth of a star and a spectacular collision of a comet with Jupiter. Images from Hubble have proved that the expansion of the universe is accelerating. Now, Hubble is near the end of its life. A new space telescope, the James Webb telescope, is planned for 2011.

Other Kinds of Telescopes

Visible light rays are only one form of electromagnetic energy that astronomical bodies emit. Other forms of electromagnetic energy that reach Earth are ultraviolet, infrared, radio, x-ray, and gamma ray energy. The energy travels through space as waves. The difference among these forms of energy is their wavelength. Wavelength is the distance between the crests of waves. Radio wavelength is longer than visible light wavelength.

Astronomers use information from ultraviolet telescopes to study extremely hot objects, such as a kind of distant star called a quasar. Infrared telescopes provide information on cooler astronomical objects, such as comets. The Hubble Space Telescope gathers ultraviolet and infrared rays as well as visible light rays.

Radio observatories are often located in remote places on Earth where the huge radio telescope dishes are free from local interference. Radio telescope dishes are concave, and some are very large. For example, the Very Large Array (VLA) in New Mexico is made of 27 movable dishes, each 25 m (82 feet) across and spread over 35 km (22 miles)! Radio waves are particularly useful for understanding an object's magnetic properties.

Even a small, inexpensive telescope lets us see remarkable details of the Moon, which is 250,000 miles away. Telescopes all of sorts have given us most of the information about the universe that we have.

DID YOU KNOW??

Microscopes were invented in the late 1500s, before telescopes.

DID YOU KNOW??

Binoculars are really two small telescope side-by-side!

DID YOU KNOW??

"Lens" comes from the Latin Word "lentil." A lens is shaped like a lentil bean.

DID YOU KNOW??

The smallest telescopes today are more powerful than the one Galileo used in 1609 to discover that the Moon has craters!

DID YOU KNOW??

Amateur telescopes capture 100 times more light than the naked eye. The biggest telescopes capture one million times more light!!

Level Pre-A

Main Concepts: We explore the concept of lenses and magnifiers.

Ask your students to find the lenses in the picture. Tell them that the lenses in WHY FLY's glasses, the magnifier, and the telescope are made of curved glass or plastic. Ask your students if they know anyone who wears eyeglasses. Why do people look through eyeglasses? Ask them if they have looked through a magnifier or a telescope. Ask them what WHY FLY is looking at through his telescope. What else could they look at through a telescope?

Vocabulary

Explain to your students that "tele" means "faraway." Tell them that "phone" means "sound" and that "vision" and "scope" mean "seeing." A telephone lets you hear sounds from faraway and televisions and telescopes let you see things that are faraway.

Weekly Lab

You need: a clear bottle with a tight cap, a penny, a newspaper, and a leaf. Tell your students to fill their bottles all the way to the top with water and put the cap on tightly. (If their bottles are glass, an adult should do this part. Make sure the bottles are completely full. lf there is an air bubble, the bottle will not act as a magnifier.) Tell them to put their bottles on their sides and place them on one of the objects. Have them look at their hand through their lens. The objects will be magnified (and distorted.) Ask them to describe what they see through the bottle. You can also have your students look at many other objects in the classroom or outside.

Math

Answers: 3; 4; 7

Storytelling

Ask students to imagine what alien life forms they might see on a new planet. Ask them if these life forms would move and if so, ask them to describe how. What colors would they be? Would they makes sounds?

Challenge

Explain that WHY FLY is looking through a magnifier at some objects. Ask your students to draw a line between the object seen with a "naked eye" (i.e., without a magnifier) and the object seen with a magnifier. Have them name the objects. Ask your students what they can see in the magnified picture that they can't see in the "naked eye" picture.

Bringing it Home

You need: a plastic bag, a glass bowl (a fish bowl works well), a drinking glass, and eyeglasses. This activity can be done at home and/or in class. Explain that lenses are pieces of curved plastic or glass. Ask your students to look at eyeglasses from the side. They will see that the lenses are curved. Ask your students to describe the shape of a water-filled plastic bag, a glass bowl, and the outside of a drinking glass. Then have them look at people or animals through these things to see how different they look. Explain that the containers act as lenses because their curved sides give the water inside a curved shape. When they look through these containers/lenses, they see things differently.

Level A

Main Concepts: We examine the concept of lenses and the use of telescopes, magnifiers and binoculars.

Picture Activity

See TN--Level Pre-A. In addition, ask students if anybody has looked through binoculars. Ask, "Why do people use binoculars?" Tell your students that some people use binoculars to identify birds, others take them to sporting events so they can see the players more clearly. Some people take them to concerts to see the musicians. Tell your students that binoculars are two little telescopes side-by-side.

Vocabulary

Answers: telescope (3), telephone (1), television (2), telegraph (4). See TN--Level Pre-A. A telegraph is a device that people once used to send written messages across long distances via wires. Explain that "graph" means "writing" and that "telegraph" means "faraway writing."

Weekly Lab

See TN--Level Pre-A. Ask students to describe what they see through the bottle. You can also have your students look at many other objects in the classroom or outside. As a class, have students discuss what they observed. Explain to them that this is something like what happens when we look through magnifying glasses, eyeglasses and telescopes, for example.

Math

Answers: Ladybug A--6 spots, colored orange; B--7, red; C--8, yellow; D--8, red; E--6 orange; F--8, yellow

Writing in Science

See TN--Level Pre--STORYTELLING. Encourage students to use their imaginations and talk about their ideas. Have them write a story about an alien life form that they might see on a new planet.

Challenge

See TN--Level Pre-A.

Bringing it Home

See TN--Level Pre-A. Encourage your students to move closer and farther away from people or pets while looking at them through their water lenses.

DID YOU KNOW??

The first lenses for eyeglasses were made in Italy in the mid-1300s.

DID YOU KNOW??

"Telescope" comes from two Greek words meaning "distance vision."

Level B

Main Concepts: We examine the characteristics of lenses and their uses.

Vocabulary

Answers: A) lenses; B) planets; C) telescopes; D) glasses

Bringing it Home

See TN--Levels Pre-A and A. Ask your students to describe the shape of their water lenses. Explain that these shapes bend the light that passes through them which makes things look different than normal. Encourage your students to move closer and farther away from people or pets while looking at them through their water lenses, and then have them describe what happens.

Math

Answers: a) 7 cm; b) 11-1/2 cm; c) 18-1/2 cm; d) 7 cm. Your students will need a metric ruler to solve these problems.

Writing in Science

See TN--Levels Pre-A and A. Ask students to write about what the surface of their planet would look like. Would there be rocks, mountains, dust, plants? Encourage them to use their imaginations and write a story describing what they might see, and draw a picture of it in the box.

Weekly Lab

You need: clear plastic food wrap; a drinking glass; clear tap water; a sheet of newspaper; and wire (Copper wire is easiest to bend, or use an unbent paper clip, or take the paper off of a twist-tie). Lab A: Have your students lightly drape the plastic sheet over the top of the glass and gently press a fist into it. It should form a pocket about half-way down the glass. Have them smooth the plastic that is not in the glass to the outside of the glass, and hold it in place with a rubber band. When they pour the water in, the plastic will assume an upside-down, down-like shape. Have your students raise and lower the glass above the newspaper to see how the words get smaller and larger. Have them also try raising and lowering the level of the water in the glass by adjusting the plastic wrap.

Lab B: The wire must cross over itself and touch, forming a loop, but there is no need to secure the end. A film of water will stay in the loop long enough for your students to hold it over a newspaper and see that the tiny water lens acts as a magnifier. Sometimes they will also be able to see that the lens turns the image upside-down. Explain that surface tension (the attraction of water molecules for each other) makes the water stay in the loop.

DID YOU KNOW??

If you looked through a six-inch telescope at one end of a football field, you could read the words on a dime on the 50-yard line?

DID YOU KNOW??

Lace makers in the early 1800s put water-filled glass spheres in front of candles. The spheres acted like lenses to focus light on their worm

Level C

Main Concepts: We examine the characteristics of lenses and their uses.

Vocabulary

Answers: 1) magnifier; 2) convex; 3) tube; 4) curved

Weekly Lab

You need: a partner, a TV (or lamp), white paper, a magnifier, and a room that can be darkened. (For this activity, a TV works best. A lamp or light bulb will work, but it will not provide as much detail. The bulb and socket will still clearly appear upside-down, though.) This lab will help illustrate how the lenses work in telescopes. A lens gathers, bends, and focuses light. Encourage your students to experiment with the distance from the magnifier to the TV (or lamp) and from the magnifier to the paper. They will see that the projected image is upside-down and reversed. Some telescopes have an additional lens or mirror that will turn the image right side-up again. Of course, since there is no up or down (or left or right) in space, it is not necessary.

Math

Answers: A) rectangles; B) pentagons; C) squares; D) triangles; E) hexagons

Writing in Science

The Internet address on page 1 of the student's level (and on page 3 of the Teaching Notes) offers a beautiful and inspiring animation of images transmitted from the Hubble Telescope from the far reaches of the universe. Help students understand that these are pictures of things no one has ever seen before. Encourage them to describe the images. Ask them to explain what the images make them think of or how it makes them feel. Give students some ideas on what their descriptions should focus.

Challenge

For Part A--you need: a piece of wire (copper wire is easiest to bend), or an unbent paper clip, and clear tap water. (Students may also try using corn syrup as an alternative.) For Part B--you need: a box of unflavored gelatin or lemon Jell-O[C]; and a variety of round-bottom containers or mold. (It is very important that your students use molds that are rounded. Many bowls have flat bottoms and will not work--although by using one, they will see for themselves that the curve is critical.) Ladles and tablespoons often have rounded bottoms. Some footed bowls do, too. Use about 75% of the water called for in the gelatin or Jell-O[R] recipe for firmer gelatin, If your students use small molds, they will not have to wait the full four hours for their lenses to set. They will probably have to run hot water on the outside of the mold or dip it in hot water to get the lens out.

Puzzle

Explain to your students that many artists use this technique to enlarge a small drawing. Encourage them to concentrate on what is in each square without thinking about how the squares fit together. It may be useful to copy the squares out of order or even upside down!

Level D

Main Concepts: We examine the characteristics of lenses and their uses.

Vocabulary

Answers: 1) magnifier; 2) reflecting; 3) refracting; 4) atmosphere; 5) eyepiece

Weekly Lab

See TN--Level C.

Math

Answers: 1) rectangles, 2) pentagons, 3) squares, 4) triangles, 5) hexagons, Bonus: octagon

Writing in Science

See TN--Level C.

Challenge

See TN--Level C.

Meet the Scientist

Dr. George Hartig is an Astronomical Instrument Scientist with the Space Telescope Science Institute in Baltimore, MD. He is also one of the original scientists who helped developed the Hubble Space Telescope. Dr. Hartig shares that he liked to build telescopes and rockets even in grade school. Currently, Dr. Hartig is studying the successor to the Hubble, the James Webb telescope which is scheduled to be launched in 2011.

DID YOU KNOW??

Telescopes can capture all kinds of energy, not just visible light. Some telescopes capture radio, infrared, or ultraviolet energy.

DID YOU KNOW??

The Hubble telescope is about the size of a tractor-trailer. The space shuttle took it aloft in 1990.

Level E

Main concepts: We examine the characteristics and use of lenses and how they change the appearance of things we see.

Vocabulary

Answers: 1) magnifier; 2) reflecting; 3) refracting; 4) atmosphere; 5) objective; 6) eyepiece

Weekly Lab

You need: a clear bottle or jar, water, and a magazine, newspaper or lined paper. For Lab A: make sure that your students have clear jars or bottles with tight caps. There must be no air in the bottles. Have them lay their bottles parallel to the lines of the text or paper. Ask them to compare their magnifier with others' to see how different bottles enlarge. In Lab B: the air bubble forms a concave space that acts as a concave lens and makes things look smaller. Ask your students to experiment by making the bubble smaller and larger and looking through it.

Math

Answers: a) 41,806.4 sq cm (6,480 sq in); b) 6.1 sq m (9,405 sq in); c) 6.3 sq yd (8,115 sq in); d) 97.5 sq ft (14,040 sq in); Bonus: 4,752 sq in;

This activity provides an excellent opportunity to do metric conversions. Answers are rounded to the nearest tenth.

Writing in Science

Explain to students that Lippershey invented the telescope, which was used to see distant things on land. Galileo made the first refracting telescope which was powerful enough to see things more clearly in the sky. He was the first to realize that there are craters on the Moon. Newton invented the reflecting telescope which was even more powerful, and used mirrors to reflect light. Newton also made important discoveries about gravity. What might he ask about the Moon? Ask students to imagine what these three great scientist might discuss if they had the opportunity to meet with other. Encourage students to use their imaginations. Suggest to them that there might be many different topics the scientists would be likely to discuss.

To extend this activity have students work in teams to write a play and have each team perform their play in front of the class.

Challenge

See TN--Level D. Part A: In addition, have your students try the experiment again using corn syrup. Part B" Encourage your students to think of other ways to make lenses. It is possible to do with ice cubes. Use distilled water for much clearer lenses. Can your students make concave lenses out of Jell-O[R] or ice? Suggest they use a tablespoon pushed down into another mold.

Meet the Scientist

See TN--Level D.

DID YOU KNOW??

Large telescopes must constantly turn so they remain pointed at objects in space as those objects move and as Earth turns!

Weekly Resources

Helpful Sources for Planning Your Science Weekly Classroom Activities

Internet Resources

* Aust, Siegfried, Nyncke, Helga. Lenses Take a Closer Look, New York: Lerner Publishing Group, 1996

* Bockneck, Jonathan. Telescopes, New York: Weigl Publishers, 2003

* Carruthers, Margaret. The Hubble Space Telescoope, New York: Scholastic Library Publishing, 2003

* Murphy, Pat. Bending Light: An Explorarium Toolbook: Dozens of Activities for Hands-On Learning, New York: Little, Brown, 1993

* Tocci, Salvatore. Experiments with a Hand Lens, New York: Scholastic Library Publishing 2002

Internet Resources

optics--http://www.opticalres.com/kidoptx.html

Lenses--http://micro.magnet.fsu.edu/optics/

Telescopes--http://www.howstuffworks.com/telescope.htm

Hubble Telescope--http://www.howstuffworks.com/hubble.htm

Lenses--http://www.howstuffworks.com/lens.htm

Microscopes--http://science.howstuffworks.com/light-microscope.htm

From Galileo to Hubble--http://amazing-space.stsci.edu/resources/explorations/galileo/

History of the Telescope--http://www.inventors.about.com/ library/inventors/bltelescope.htm

Galileo and the Telescope--http://www.pbs.org /wgbh/nova/galileo/telescope.html

Incredible pictures from the Hubble telescope (animated slide show) --http://wires.news.com.au/special/mm/030811-hubble.htm

Powers of 10 in outer space (Here is another very interesting animated image)--http://micro.magnet.fsu.edu/primer/java/scienceopticsu /powersof10/index.html

Telescopes and Lenses

Level C

Why Do We Need Lenses?

Lenses change the way things look. They can make things look larger or smaller or clearer. We see things during the day because light bounces off the objects or things we see. We can't see in the dark because there is no light to bounce off of things. Since lenses are curved pieces of glass or plastic, they bend the light before it reaches your eyes. Eyeglasses have lenses that help you see.

Making Small Things Look Larger

A magnifier is a lens that makes small things look larger. It has a convex (con-vex) lens which curves outward and is shaped like a dome.

Making Far-Away Things Look Closer

Telescopes make stars, planets, and the moon appear closer. Telescopes have two lenses in a long tube, one at each end. The lens at the far end gathers light and sends a picture down the tube. The lens at the near end is called the eyepiece lens. The eyepiece magnifies the picture.

The largest telescopes are reflecting telescopes. They use curved mirrors instead of lenses to gather light. The Hubble Space Telescope is the world's best telescope. It circles the Earth in space.

DID YOU KNOW??

"Telescope" comes from two Greek words meaning "distance vision."

DID YOU KNOW??

"Lens" comes from the Latin Word "lentil." A lens is shaped like a lentil bean.

Vocabulary

Can you finish these sentences about lenses and telescopes?

1. A--is a lens that makes small things look large

2. A--lens curves outward and is shaped like a dome.

3. Telescopes have two lenses in a long--, one at each end.

4. The Hubble is a reflecting telescope that uses--mirrors.

Adult Supervision Recommended

Weekly Lab

How does a magnifier work? Let's see!

You need: a partner, a TV, white-paper, a magnifier, and a room that can be darkened

Step 1: Turn on the TV and darken the room.

Step 2: Have your partner hold the white paper about 1 meter (3 feet) from the TV.

Step 3: Then, hold the magnifier close to the white paper.

Step 4: What do you predict will happen when you move your magnifier away from the paper towards the TV?

Step 5: Then, slowly move the magnifier farther away from the white paper towards the TV. Do this until you get a clear picture on the white paper. What do you see? Is this what you thought would happen?

DID YOU KNOW??

Your eye has a convex lens, too. Muscles in your eye move the lens so you can focus!

Math

The mirrors of the largest reflecting telescopes are made of many small mirrors placed next to each other. Match the shapes of each mirror to the words.

DID YOU KNOW??

Instead of one mirror, The California Extremely Large Telescope will have 1,080 hexagonal mirrors.

Writing in Science

Go to the Internet to see some incredible pictures from the Hubble Space Telescope. In one or two paragraphs describe what you saw.

DID YOU KNOW??

The Hubble telescope orbits the Earth once every 97 minutes!

DID YOU KNOW??

The Hubble telescope is so powerful because its mirror catches light before light gets distorted by our atmosphere!

DID YOU KNOW??

The Hubble telescope is about the size of a tractor-trailer. The space shuttle took it aloft in 1990.

Adult Supervision Recommended

Challenge

You can make lots of different kinds of magnifiers! See which one you like best.

You need: a piece of wire (copper wire works best) or an unbent paper clip; a pencil; a cup of water; a box of unflavored gelatin or lemon Jell-O[R]; a newspaper or magazine; and, round molds of various kinds (i.e. a large ladle or round spoon)

A. Make a water lens! Bend a piece of wire around a pencil to make a circle. Dip it in water. Look at a newspaper through the water lens!

B. Make Jell-O[R] lenses! Ask your teacher or parent to help you prepare unflavored gelatin or lemon Jell-O[R] according to the directions, except use a little less water. Pour it into rounded molds of different sizes. Cool them in the refrigerator.

C. Which magnifier did you like best? Write a paragraph about why you like one better than the other.

Use molds that are shaped like half a ball.

Try corn syrup instead of water!

Puzzle

Galileo was the first person to point a telescope at the skies. Magnify this picture of Galileo by drawing each block in the larger, matching square.

DID YOU KNOW??

Galileo was the first person to use a telescope to look at the sky in 1609.

DID YOU KNOW??

Lace makers in the early 1800s put water-filled glass spheres in front of candles. The spheres acted like lenses to focus light on their work!

To see some incredible pictures from the Hubble Space Telescope go to: http://wires.news.com.au/special/mm/030811-hubble.htm
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Date:Feb 14, 2005
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