Light Telescopes Grade Level: 5 Time Required: Suggested TEKS: Science - 5.4 Suggested SCANS Information. Acquires and evaluates information. National Science and Math Standards Science as Inquiry, Earth and Space Science, Science and Technology, Physical Science, Measurement, Observing, Communicating 2-3 class periods (more if in-depth research occurs) Countdown: 2 cardboard tubes (i.e., toilet paper, paper towel if cut down to less than toilet paper tube) 2 convex lenses, 1 thick and 1 thin Ignition: Early astronomers depended on the human eye to study the visible stars and the patterns they made. They discovered five planets and the patterns they made. But, the true nature of celestial objects awaited the invention of the telescope in 1609. A telescope is defined as an instrument that makes distant objects nearer and larger. A simple kind of telescope is made of two tubes and three lenses. One of the tubes fits inside the other. A large glass lens, called the objective, is at one end of the tubes. It points at the object to be viewed. The eyepiece, located at the other end, is held to the eye, magnifying the image. All objects give off light. Light travels in light waves in straight lines. Therefore, light waves travel from the object being observed to the telescope. The light waves pass through the objective and into the tube of the telescope. Depending on the type of telescope used, the image appears upside down. Halfway down the tube is the middle lens, which bends the light waves to turn the image right side up. The observer views the image through the eyepiece, right side up. Liftoff: A. Discussion 1. The refracting telescope Discuss with the students that one kind of optical telescope is the refracting telescope. This telescope uses glass lenses to focus light directly into the eyepiece. Note the diagram below. The largest refracting telescope is located at the Yerkes Observatory in Wisconsin. Unfortunately, the lenses had to be restricted to a width size of 40 inches because greater sizes caused them to sag. 84
Refracting Telescope Lens Light Waves Eyepiece Eyepiece 2. The reflecting telescope Discuss that another kind of optical telescope is the reflecting telescope. These telescope uses curved mirrors which bounce off light to each other, then send it to the eyepiece. See diagram below. Big telescopes, like the Hubble with its 94.5 inch mirror and the Hale telescope with its 200-inch mirror, are reflecting telescopes that can gather a tremendous amount of light. When coupled with an electronic camera, they can see galaxies billions of miles away. Reflecting Telescope Light Waves Eyepiece Mirror Mirror 85
3. The solar telescope A solar telescope is specifically designed to observe the details of our blazing Sun. It has an extremely long focal length in order to focus on areas just 100 miles wide. The McMath telescope, located in Arizona, is the size of a 50-story building laid on its side. The 11-story tower, built above ground, allows sunlight to enter undisturbed by air turbulence near the ground. The light strikes a movable flat mirror that follows the Sun; then it is beamed to a concave mirror at the bottom of the shaft. From there, it is reflected to another mirror and then into the observation room. 4. The coronagraph A coronagraph is a special type of optical telescope that helps astronomers to see the corona, the Sun s thin upper atmosphere. Because the corona can only be seen when the brilliant light from the Sun s surface is blocked out, the coronagraph has a disk in its tube that creates an artificial eclipse. Skylab in 1973 photographed the corona. In this photograph, the corona extends twice the Sun s diameter. 5. The radio telescope Discuss that a radio telescope sees the long wavelength waves, emitted by celestial bodies that make up the radio end of a spectrum. The mirror of a radio telescope is a huge saucer-shaped reflector. See diagram below. The National Radio Astronomy Observatory, located in Socorro, New Mexico, utilizes several radio telescopes. The Radio Telescope B. Activities 1. Make a simple refracting telescope a. Slide the smaller paper towel tube inside the slightly larger toilet paper tube. The tubes need to fit snugly. b. To the outside of the smaller tube, attach the thick convex lens. To the outside of the larger tube, attach the thin convex lens. See diagram below. paper towel tube toilet paper tube thick convex lens (eyepiece) thin convex lens (objective) 86
c. Look through the eyepiece lens, and slide the tubes in and out until the object being viewed comes into focus. 2. Categorize the different kind of telescopes. Have students complete the attached table (sample below) according to information given in Part A. Kind of Telescope What is used to focus Light Identifying Feature When Used 3. Divide the students into groups. Each group will work on one of the following activities and give an oral presentation. a. Research the Hubble Space Telescope. Students will record findings, write a research paper, drawings, and report back to the class. According to the February 1998 issue of Discover, the space shuttle will pay its fourth and final maintenance visit to the Hubble Space Telescope in March 2002. Thereafter, its famed work will soon be completed. As is true with modern computer technology, the amazing Hubble s capabilities are actually beginning to seem a little limited: 1) its mirror is too small 2) its focus is too narrow 3) its heat is too obscuring 4) its earth orbit is too crowded 5) its blindness extends to half the light of the sky (i.e. gamma rays, ultraviolet, and radio waves) NASA-sponsored lab plans for the future are not to replace the Hubble, but rather to improve it. New technologies will overcome the obstacles and limitations of the Hubble, as well as answer far-reaching questions such as whether life exists elsewhere in the universe. b. Research NASA s future plans for space telescopes and missions If all goes according to schedule, NASA will introduce Space Infrared Telescope Facility (SIRTF) in 2001. Some of the features are as follows: 1) it will contain enough liquid helium to keep its temperature at 450 degrees below zero Fahrenheit (this will allow it to view infrared light) 2) it will orbit the Sun, rather than the Earth 3) it will have a 33-inch mirror and infrared-sensitive detectors 4) it will be able to spot superplanets and brown dwarfs 5) it will be able to examine the birthplaces and cemeteries of stars and provide information about how galaxies are formed 6) it may be able to pick up signs of carbon and water vapor in the disks of dust around the stars, thereby suggesting other life-supporting planets NASA has plans to launch three other space telescopes: 87
Space Interferometry Mission (SIM) in March 2005 NASA Generation Space Telescope (NGST) around 2007 Terrestrial Planet Finder (TPF) around 2013 As part of its Origins program, NASA is also planning four pre-cursor missions by 2001. They are as follows: Wide-Field Infrared Explorer (WIRE) Far Ultraviolet Spectroscopic Explorer (FUSE) Stratospheric Observatory for Infrared Astronomy (SOFIA) New Millennium Interferometer (NMI) c. Locate the Southwest Observatories and Observe the Night Sky Suggestions for information include: StarDate Productions (800-STARDATE) Or write to StarDATE, 2609 University Avenue, #3,118, Austin, TX 78712 Web Site: http://stardate.utexas.edu World Wide Web listing in Appendix 88
Telescopes Kind of Telescope What is used to focus Light Identifying Feature When Used 89