TELESCOPES An overview of the main tools used by astronomers to study the universe.

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1 Lesson 203: TELESCOPES An overview of the main tools used by astronomers to study the universe. Fundamental Questions Attempting to give thorough and reasonable answers to the following questions will help you gauge your level of understanding this lesson. Students that can confidently answer these questions have mastered the concepts of this lesson. 1. What is the best kind of telescope to view a distant galaxy and why? 2. Why are orbiting space telescopes generally better than earth-based telescopes? 3. Why haven't we built a telescope that is capable of seeing everything in the universe? 4. What is the most powerful telescope in the world? Lesson Objectives At the end of this lesson, students should have mastered the objectives listed below. 1. Students can illustrate the inner workings and parts of both types of optical telescopes and can explain why the image that is seen in an optical telescope is upside-down. 2. Students understand the problems with building large lenses/mirrors. 3. Students know which types of electromagnetic radiation are blocked/absorbed by our atmosphere and also know which kinds of telescopes need to be located in space to view these types of light. 4. Students are aware that radio telescopes are sometimes used to search for extraterrestrials. 5. Students can describe the basic designs and advantages of the Hubble Space Telescope, the VLA, the VLT, the LBT, and the Keck Telescope. 6. Students understand the advantages of reflecting telescopes over refracting telescopes for viewing distant, dim objects. 7. Students understand that glass is an amorphous substance, which means it flows like a liquid due to the force of gravity. 8. * Intensive/Honors students can determine the magnification of telescopes by dividing the telescope's focal length by the eyepiece's focal length. Important Terms The following terms are some of the vocabulary that students should be familiar with in order to fully master this lesson. 1. amorphous 2. angle of incidence 3. angle of reflection 4. aperature 5. focal length 6. focus 7. Galileo 8. Hubble Space Telescope Assessment Questions 9. interferometer 10. Keck telescope 11. Large Binocular Telescope (LBT) 12. Multiple-mirror Reflecting Telescope 13. optical 14. reflecting 15. refracting 16. SETI 17. solar telescope 18. Very Large Array (VLA) telescope 19. Very Large Telescope (VLT) The following are examples of questions that students should be able to answer. These or similar questions are likely to appear on the exam. 1. What is meant by "the aperature" of a telescope? 2. * What is the magnification of a telescope that has a focal length of 1000mm and an eyepiece focal length of 10mm? 3. What is a multiple mirror reflecting telescope and why are they used? 4. What is an interfermoter and why are they used in astronomy? 5. Give three examples of multiple mirror reflecting telescopes. Where are they located? 6. Give three examples of interferometers. Where are they located? 7. Why are reflecting telescopes generally considered better than refracting telescopes for astronomy? 8. What is SETI and what kinds of telescopes do they use? 9. Describe the Hubble Space Telescope. 10. Why haven't we built a telescope that is capable of seeing everything in the universe? 11. How does a refracting telescope work? 12. Why do space telescopes obtain clearer images than ground-based telescopes? 1

2 13. * If you want to increase the magnification of a telescope, should you increase or decrease the focal length of the eyepiece? Related Web Sites The following are some web sites that are related to this lesson. You are encouraged to check out these sites to obtain additional information Related Book Pages The following are the pages from your book that correspond to this lesson. Massachusetts Standards Comprehensive E.S. Book Intensive/Honors E.S. Book Meteorology/GIS Book pp pp NA The following are the Massachusetts Framework Standards that correspond to this lesson. Earth Science Learning Standard(s) 1.2, 1.3, 4.1 What s Next? Notes 2

3 XIX. TYPES OF TELESCOPES A. Optical Telescopes optical refers to light 1. Refracting Telescopes a. older style of telescope with eyepiece at opposite end from where light enters b. uses only lenses to focus and magnify light c. larger lenses generally mean greater light-gathering power d. 40-inch Yerkes Observatory in Wisconsin is largest in world 2. Reflecting Telescopes a. uses mainly mirrors to focus and magnify light b. mirrors can be made much larger than lenses, up to about 5 meters (200 inches) diameter c. 200-inch Hale telescope in California is world s largest Notes on Telescopes October 4, 2002 Page 1 of 2

4 3. Multiple Mirror Reflecting Telescopes a. similar to a regular reflecting telescope, but uses more than one mirror to collect light thereby increasing the amount of light that the telescope can collect b. Keck telescope in Hawaii is world s largest multiple mirror reflecting telescope, having 36 segments of mirror that combine to make a 400-inch mirror B. Radio Telescopes 1. Use a metal dish to collect radio waves, rather than lenses or mirrors 2. Used to search for extraterrestrial life and to study radio waves that are emitted by stars and other objects 3. The Very Large Array (VLA) radio telescopes in New Mexico consists of 27 separate radio telescopes that can be used at the same time (as an interferometer), similar to a multiple mirror telescope C. Infrared Telescopes 1. All objects that have mass give off infrared radiation 2. Used to detect dusts and gases that other telescopes cannot see 3. Infrared telescopes orbit the earth in space because earth-based telescopes would detect all of the infrared radiation in the atmosphere D. Ultraviolet Telescopes 1. Used to detect UV rays 2. UV telescopes orbit the earth in space because earth-based telescopes would detect all of the UV radiation in the atmosphere E. X-ray Telescopes 1. Almost all stars give off x-rays 2. Used to study the life cycle of stars 3. X-ray telescopes orbit the earth in space because x-rays do not easily pass through the earth s atmosphere F. The Hubble Space Telescope 1. The Hubble Space Telescope orbits the earth and is capable of obtaining images of objects emitting most forms of light. 2. Overall, it is the most advanced and best telescope that we have available right now. 3. The mirror of this telescope is 2.5 meters in diameter. 4. Data collected by this telescope is changing the face of astronomy. Notes on Telescopes October 4, 2002 Page 2 of 2

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9 40-inch Yerkes Refracting Telescope in Wisconsin. Built in Newtonian Reflector Maksutov-Cassegrain Dobsonian Reflector The Hale Reflecting Telescope in California 1

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