How Does a Refracting Telescope Work?
A refracting telescope works just like a magnifying glass. It uses a convex glass lens (to bend light and bring it into focus. This lens is thicker in the center than it is toward its edges, which bends the light more at the edge of the lens than light coming through the center. This allows all of the light to come together at a focus point. The point of focus is where the image is created.
If someone looks into the eyepiece, a concave lens magnifies the image.
Refracting telescopes have two main problems—images are not always clear because the light is being bent and the size of the lens is limited (which limits the power of the telescope).
History of the Refracting Telescope
A Dutch optician (someone who makes lenses for glasses), Hans Lippershey, designed the convex lens for the first refracting telescope in 1608. He found that a distant object appeared to be much closer when he looked at it through a concave lens and a convex lens held in front of each other. He put the lenses into a tube to make the first refracting telescope.
Galileo Galilee made the first refracting telescope used to study space in 1609. He used it to discover four of the moons orbiting Jupiter. Galileo also used his refracting telescope to map the surface of the moon. Galileo could see objects 20 times smaller than the human eye could using his telescope.
How Does a Reflecting Telescope Work?
Reflecting telescopes use curved mirrors instead of convex lenses to collect and focus light. A large concave mirror (the center is thinner than the edges) collects and reflects the light to make an image. Once the image forms, the lens in the eyepiece magnifies the image. Reflecting telescopes are very helpful for viewing dim or dark objects. Large reflecting telescopes can see objects that are a millionth or a billionth the brightness of the faintest star that can be seen by the human eye alone!
History of the Reflecting Telescope
A Scottish astronomer, James Gregory, came up with the design for the reflecting telescope in 1663. Isaac Newton made the first model of the reflecting telescope in 1688. After Newton built the model, scientists discovered that better images are seen through the reflecting telescope instead of the refracting telescope because mirrors could make clearer images since the mirrors could be made much larger than the lenses. The reflecting telescope is still used today.
Unless otherwise noted, all images courtesy of NASA. Permission for use at http://www.nasa.gov/gallery/photo/guideline.html.
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