how to build a simple refracting telescope

How to build a simple refracting telescope by putting together the right combination of lenses. No one knows who first did it.

Science.aksiografi.com – No one knows who first put together the right combination of lenses to make the first telescope (an instrument used to make distant objects appear nearer and larger). One story is that some children playing in an Amsterdam optical shop owned by the Dutch spectacle maker Hans Lippershey (c.1570–1619), happened to look through two lenses at the same time and saw an amazing magnified world.

Another story says that Lippershey himself made the discovery. In any case, Lippershey improved on the discovery by putting two lenses in a tube, one at each end. He called the invention a “looker” and sold them in his shop. Lippershey’s “looker” was used as a telescope to view distant objects as well as a micro-scope, which is an instrument used to magnify tiny or microscopic (not visible to the naked eye) objects.

Others say that the Dutch spectacle maker Zacharias Janssen (1580–1638) was the inventor of both the telescope and the compound microscope (microscope with two or more lenses). Whoever first came up with the idea, we know that it happened sometime in the early 1600s. As with many inventions, it is possible that several people independently discovered the magnifying effect of using two lenses. Galileo, is often given credit for the invention of the telescope, as well as for being the first person to study the sky with the instrument.

Galileo didn’t invent the telescope, but he did make improvements. And Galileo may not have been the first to use a telescope to observe the sky, but he was the first to report astronomical discoveries made with a telescope, such as the fact that Jupiter has moons.

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The first Galilean telescope was made in the summer of 1609 with a lead pipe. It had a magnification of 3×, which means it magnified things so that they looked three times nearer as when viewed with the naked eye. Galileo continued to improve and increase the magnification of his telescopes. Later Galilean models were about 30×, which was 10 times the magnification of his first model, so it made things look 30 times nearer.

Today, many telescopes use an arrangement of lenses that gathers light and forms an image of an object. An image is a likeness of an object. Designed in 1611 by Johanes Kepler, this instrument is called a refracting telescope or Keplerian telescope. A Keplerian telescope provides greater magnification than a Galilean telescope, but the lenses used caused images to be upside down.

In 1721, Isaac Newton improved the design of the telescope by using a combination of a mirror and a lens. This is called a reflecting telescope or Newtonian telescope. Today the largest telescope on Earth is the Keck Telescope, which is a reflecting telescope. The mirror that is pointed toward the sky and gathers light is made up of 36 mirrors, each measuring about 6 feet 7 inches (2 m) across. The Hubble Space Telescope (HST), with a lightgathering mirror about 8 feet (2.4 m) across, is a reflecting telescope that orbits the Earth. It was launched on April 25, 1990, and is used to observe distant objects in space.

Learning Objectives

To build a simple refracting telescope.

Materials

masking tape

sheet of newspaper with some large print

2 magnifying lenses

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Procedure

1. Tape the newspaper to a wall at eye level.

2. Pace off three steps from the newspaper, then turn and face the paper.

3. Close one eye and hold one of the magnifying lenses in front of your open eye.

4. Hold the second lens directly in front of the first lens.

5. Slowly move the second lens toward the newspaper until a clear image of the large print on the paper is seen.

figure how to use teleschope

Results

Print on the newspaper appears enlarged and upside down.

Why?

The image seen through the two lenses is similar to images viewed through a simple refracting telescope. The parts of a refracting telescope can be compared to the lenses in this investigation. The lens farther from the eye behaves similarly to the objective lens of a refracting telescope. This is the lens that faces the object being viewed and gathers the light. The objective lens produces an inverted (upside-down) image near a point within the telescope where the light rays come together, called the focal point. The eyepiece, which is the lens you look through, magnifies the image formed by the objective lens and sends this enlarged image to your eye. A reflecting telescope works in a similar way except that mirrors gather and direct the image to the focal point, where it is magnified by the eyepiece.

figure a child using teleschope to see closer the stars

Try New Approaches

Binoculars are actually two simple telescopes that are connected. Binoculars produce upright images because they have prisms (solid see-through materials that change the direction of light passing through.) inside, which turn the upside-down image back upright. Use binoculars to study different celestial bodies in the night-time sky. Try to find the moons around Jupiter or the craters on the Moon. (To get information about the celestial bodies visible on any specific night, see an astronomy magazine, such as Sky & Telescope.)

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References

Matloff, Gregory. Telescope Power. New York: Wiley, 1993. Information about telescopes, including fun activities and projects.

Schultz, Ron. Looking Inside Telescopes and the Night Sky. Santa Fe, N.M.: John Muir Publishing, 1992. Describes different kinds of telescopes, how they work, and what they tell us about the universe.

Scott, Elaine. Close Encounters: Exploring the Universe with the Hubble Space Telescope. New York: Disney Press, 1998. Explains what scientists have learned about our solar system and the universe from information collected by the Hubble Space Telescope.

VanCleave, Janice. Janice VanCleave’s Help! My Science Project Is Due Tomorrow! Hoboken, N.J.: Wiley, 2002. Easy science projects, including ones about telescopes, that you can do overnight.

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