## Exhibit Concepts Developed by NRAO staff and Project Advisory Committee

Exhibit Group One. Exploring the Question: What are Radio Waves?

Exhibit #1 Concept: A moving charge like a spark produces EM radiation

This exhibit will use a spark plug, receiver and spectrum analyzer to approximate Hertz's experiment in which he discovered radio waves. A spark plug is set up to give off a spark when the visitor pushes a button. A receiver positioned at some distance away will audibly register the signal. The spectrum analyzer will show spikes occurring at many different frequencies indicating radio emission.

Spark plugs are a source of man-made radio waves which interfere with the radio telescopes at NRAO. We prohibit most vehicles with spark plugs from driving on the site. Because this exhibit could really cause interference at the telescopes, the exhibit will have to be shielded in a Faraday cage. Thus, this exhibit can be used to teach visitors that interference is important and needs to be controlled at the NRAO.

Outcome: An accelerated charge like a spark from a spark plug produces radio waves. Radio waves cannot pass through a wire enclosure.

Exhibit #2 Concept: Radio waves and light waves are fundamentally the same. (Nature's Spark)

To illustrate the fundamental similarity of light and radio waves a thunder storm and a radio will be videotaped. When lightning flashes, static is immediately heard on the radio, but the thunder is not heard for some seconds depending on how far away the lightning struck. The static results from the transmission of radio wave traveling at C. The thunder travels at the speed of sound The visitor will be prompted to predict the order of events before playing the short video segment

Outcome: Radio waves travel at the speed of light, not the speed of sound.

Exhibit #3 Concept: Electromagnetic waves and sound waves are different.

A bell and a spark plug will be placed inside a bell jar. When both are activated they can be detected, the bell by sound and the spark also by static heard in a receiver. A vacuum is then created in the bell jar. Radio waves are still detected in the receiver. However, sound from the bell cannot be heard.

Outcome: Sound waves require a medium, radio waves do not. They are self propagating.

Exhibit #4 Concept : Radio waves are part of the electromagnetic spectrum

The electromagnetic spectrum will be depicted in a wall mural. Astronomical images formed from data taken at each wavelength will be displayed. The instruments used to collect astronomical data will be illustrated. In addition, information about wavelength, frequency, energy will be presented.

Since the Orion Constellation is an easily recognized constellation, it will be used as the basis for astronomical image displays. The region is diverse and interesting at many wavelengths.

Outcome: Visible light makes up a fraction of all electromagnetic energy. Wavelength and frequency are defined.

Exhibit Group 2. Exploring the Question: How do we Detect Radio Waves?

Exhibit #1 Concept: Different parts of the electromagnetic spectrum are detected in different ways.

The eye is a natural detector of light. A display may show how the eye works. For other wavelengths of EM radiation different strategies must be developed. Infrared detectors will form the base of this exhibit. Infrared radiation can be sensed by visitors but not "seen". Visitors experiencing how such radiation is detected will draw fairly accurate analogies about how radio astronomy is done. Several stations could be planned around this theme. For example: infrared detectors operating around 2 microns will display warmer objects as white and cooler ones black. Familiar objects around the room, not optically bright, may be quite bright in the infrared. In addition, heat sensitive liquid crystal panels are inexpensive detectors of IR. Black light and UV sensitive materials can illustrate the detection of UV radiation.

A wall display of the EM spectrum in wavelength along the x axis and altitude along the y axis, illustrated by a cross section through a landscape from sea level to Mt. Everest will illustrate which wavelengths of energy penetrate to the earth's surface and which must be investigated

Outcome: Manmade detectors extend our senses.

Exhibit #2 Concept: Mystery boxes: extending our senses

Covered "shoeboxes" will contain objects which can not be identified by sight. The boxes will have a grid of small holes along the top. Children can shake the boxes, and systematically probe the inside with dowels. They can then attempt to match the object in their box to an object in a photograph.

Exhibit #3 Concept: Parabolic reflectors are mirrors: radio waves striking their surface may be focused to a point.

This exhibit will be a lesson in optics. Many small (1 cm. square) flat mirrors will be mounted so as to move to fixed locations in one of three configurations: a symmetrical parabola, a portion of a sphere or, like the GBT, with an offset design. Rays of light will be produced which will strike the mirrors and form a focus.

Visitors can observe changes in the focused light from a focal point above the center of the symmetrical parabola, to a focal line with the spherical section, to a focal point offset from the center with the GBT like configuration. Visitors can experiment with obstructions like feed support legs, so that they get a feel for why we are building offset telescope like the GBT. Other manipulatives can include a GBT-like offset arm, complete with a secondary mirror that will redirect the light to a "receiver room". Design diagrams of the GBT, along with data showing the effects of feed legs on the response of a telescope will also be displayed.

The Infrared connection can be explored here also. A parabolic mirror will focus heat to a point. This can be detected by your hand.

Outcomes: Parabolic mirrors focus EM waves to a point thereby increasing the detected signal strength. The GBT is a piece of a parabola and works just as well as a symmetrical parabola. The location of the focus is moved advantageously.

Exhibit #4 Concept: Wavy mirrors

Children can change the shape of life sized flexible mylar mirrors and observe changes in their reflection.

Exhibit #5 Concept: Parabolic basketball , Whisper dishes

A parabolic dish will be fitted with a basketball hoop at the focal point. Children can use Nerf balls to shoot hoops. Whisper dishes place at opposite ends of a field will illustrate the concept of focal point

Exhibit #6 Concept: How are images of a radio source produced?

a. Chart recordings are an old fashioned way to collect data but a way that is intuitive to visitors. This video display would take visitors through the steps of creating a false color radio image beginning with collecting chart recordings from successive declination intervals in the sky. These chart recordings can be converted into columns of numbers which could then be used to generate a false color contour map.

* Try it at Home sheet: Visitors can obtain a pixel grid to color for themselves.

b. Image puzzles will be made of thick wooden pieces each representing a "slice" through an image. when assembled in the right order a 3-D representation of the object results. Radio objects are also represented by contour maps showing levels of intensity. Contour map puzzles can be created using flat colored wooden piece shaped for each contour level. When the puzzle is assembled it will resemble the image when viewed from top down.

Outcome: visitors understand how radio "pictures" are created.

Exhibit #7: Putting it all together: A Working Radio Telescope

This exhibit will be a working 2 foot diameter parabolic radio telescope that will scan the sun. Data will be recorded with a chart recorder. Visitors can use the telescope and take the chart recording home with them. They can also place their hands between the dish and the focal point. They will see a rise in intensity on the chart recorder. People emit radio waves. The emission process is thermal.

Outcomes: Visitors synthesize the entire process of detecting radio waves from space. Visitors participate in science by using a radio telescope.

Exhibit Group 3. Exploring the Question: What can Radio Astronomy tell us about the Universe?

Exhibit #1 Concept: Light is Our Only Tool for Studying the Universe

This exhibit would allow visitors to observe and graph continuum and spectral line radiation from light sources and radio sources. The spectrum produced by an incandescent bulb can be displayed on a monitor allowing visitors to see that the emission is a blackbody curve continuous over a range of wavelengths. Visitors will also note that the peak emission is in the infrared, rather than in the visible. They can compare this spectrum graph to others of hotter objects, and to astronomical objects like a star, or the cosmic microwave background. Thermal continuous spectra can be compared to non-thermal spectra such as exhibited by most radio sources.

Finally, emission and absorption spectral lines can be observed using gas spectrum tubes in the visible part of the spectrum, and spectroscopes. Visitors will for example observe the spectral lines produced by a mercury spectrum tube, then be asked to observe a florescent light. They will determine the presence of mercury indirectly, just as astronomers determine the presence of elements and molecules in the universe.

Exhibit #2 Optical Astronomy and Radio Astronomy give different clues about the universe

Optical astronomy is familiar. We plan to use a combination of displays to compare astronomy at optical and radio wavelengths:

· An optical telescope or heliostat will display an optical image of the sun for comparison to the radio data obtained with the 2 foot radio telescope. When the sun is behind the clouds and light cannot pass, this will illustrate that radio waves are not blocked by clouds.

· Hands On Universe Image Processing software will allow visitors to call up optical and radio images of the same object. Examples of objects that appear different at the two wavelengths include: the Sun, Saturn, Jupiter, supernova remnants, radio galaxies, stars, the Galactic center. and Orion. Visitors can try to predict or match optical images with their radio counterparts before conducting the investigations.

Outcome: Exhibits contrasting objects in the radio with their appearance at optical wavelengths illustrate the value of radio astronomy.

Exhibit #3 Concept: Investigating the lives of stars

This exhibit will illustrate the life cycle of a star, and be linked with exhibits on stellar nurseries and the products of star death: heavy elements created in supernova explosions, and pulsars.

a. Star Forming Regions: Detecting Molecules in the Interstellar Medium

This exhibit would allow visitors to discover the similarities between visible bright line spectra and radio spectra. The visitor will be guided to equate the Interstellar medium with a combination of rarefied gases like a neon light. Much radio astronomical research is directed toward understanding star forming regions in the ISM. This research will be highlighted.

b. Pulsars : Radio Light Houses

This exhibit will be a mechanical model of a pulsar. A visitor can choose a pulsar, learn where it is in the sky and hear an audio recording of the pulsed static emitted by the pulsar. The mechanical pulsar will rotate with the appropriate period to produce the signal. What is known and unknown about pulsars will be listed. Selected pulsars can be located on a map of the sky by a light at the proper coordinates which blinks with the period of the pulsar when it is selected.

Exhibit #4 Concept: Measuring Distance: Doppler shift

A whistle on the end of a rotating arm will change pitch as it rotates around. A water tank may be used to demonstrate how wavelength can be Doppler shifted to shorter and longer wavelengths

Exhibit #5: Mapping the Milky Way

Astronomers map the neutral hydrogen (HI) in our Galaxy by detecting its spectral line emission at 21 cm. In this exhibit visitors will determine the connection between Doppler shift in spectral lines and velocity measurements. Using real HI radio spectra, visitors will determine the velocity of HI gas toward us and away from us. The rotation of the Milky Way can be inferred. HI spectra of other galaxies show that they are also rotating.

Outcome: Visitors will learn that motions can be detected by measuring the Doppler shift in spectral line radiation.

Exhibit #6: Mapping the Large Scale structure of the universe; Is matter smoothly distributed on large scales?

Galaxies like our own contain neutral Hydrogen (HI). By looking at the spectral line profiles of several galaxies visitors will be able to classify them into two groups: those with double peaks and those with single peaks. Spectral line profiles with double peaks indicate a rotating galaxy that is seen edge on with respect to earth. The double peaks are cause by the Doppler shift. Visitors will begin to predict if a galaxy is edge on or face on by associating a few spectra with a photograph of the corresponding galaxy. Astronomers use the Doppler shift of HI emission to estimate distances to galaxies. When positions are mapped, galaxies appear to be unevenly distributed. The assumptions astronomers must make to estimate these distances will be emphasized.

Exhibit #7: Serendipitous Discoveries in Radio Astronomy

Would you recognize a new phenomenon if you were looking for something else? Visitors will search for the telltale anomalies in data that were noticed by scientists, leading to major discoveries in radio astronomy. Data such as that collected by Jocelyn Bell, which led to the discovery of pulsars, Karl Jansky, which led to the discovery of radio waves from space, and Bernard Burke, which led to the discovery of radio emission from Jupiter will be displayed. The discovery of the binary pulsar for which Joe Taylor and Russ Hulse shared the 1993 Nobel Prize is a recent example. Logbook entries made by then graduate student Russ Hulse reveal a dawning awareness that his data was not in error, but in fact an incredible discovery.

Exhibit #8: The Search for Extra-Terrestrial Intelligence (SETI)

This exhibit will focus on the history of SETI, its beginning in Green Bank and how a search is conducted. The assumptions astronomers make in order to set parameters on a search will be described. Astronomers dedicated to SETI will be profiled. The SETI Institute will be using the 140 Foot telescope after the GBT is operational and will fund this exhibit.

Exhibit Group 4. Exploring the Question: What is going on at the Telescopes now?

Exhibit #1: Who is Using the Telescopes?

This exhibit will be an on-line computer telescope schedule. Interactive programs will allow visitors to learn where the telescopes are pointing, what is in that part of the sky, who the current users of the telescope are and what they hope to learn. This exhibit will emphasize the ongoing investigative nature of scientific research. Astronomers will be asked to create an on-line "dossier" which includes information on:

• How they got interested in science;
• The questions they hope to answer through their research;
• What they don't know about the topic they are studying;
• How long will they work on this topic in order to answer the questions they have.

Exhibit #2 Concept: Real-time Data:

Visitors will be linked to astronomers' terminal via ethernet so that they can see data being collected by the GBT, 85 Foot Telescope data from the Berkeley/Princeton/Oberlin Pulsar experiment, and SETI data. The visitor will determine the area of sky under observation and be able to access a planetarium program which allows them to explore that region of sky.

Exhibit Group 5. Exploring the Role of Technology in Science

Exhibit #1 Concept: How does a receiver work?

An oversized receiver will be built in which components: amplifier, filters, local oscillator, mixer etc. are labeled. These parts can be exchanged for similar parts of different characteristics. An output spectrum analyzer will show the effects of changes made. For example, a visitor might exchange an amplifier for a "bad" one that is less sensitive or more noisy. Filters could be exchanged that change the frequency response of the receiver.

Visitors may collect a toolbox which has interchangeable parts and a voltmeter and given the task to "fix" the receiver.

Outcome: The different parts of a receiver have different functions.

Exhibit #2 Concept: Cryogenically cooling our amplifiers improves them.

A simple exhibit will be built that shows liquid nitrogen reduces the resistance through a coil of wire in a circuit. The circuit might terminate in a light bulb. When the wire is cooled, the bulb glows brighter.

Exhibit #3: Virtual Walk through of the GBT

Apple Computer, Inc. has developed a "software authoring package", Quicktime Virtual Reality, that makes it possible to create panoramic and object virtual reality movies from digitized photographs, video, and computer graphic images. NRAO has purchased this package and intends to develop a Quicktime movie by compiling digital photographs of the GBT taken from different perspectives from top to bottom. The movie will allow the viewer to take a virtual tour of the Green Bank Telescope- visiting any structure on the telescope- choosing his/her path and view by clicking the mouse. Visitors will be able to "see" the view from atop the GBT subreflector 480 feet up, walk through the receiver room, look down on the reflector or view the maze of beams in the support structure.

Exhibit #4 Concept: Illustrating the role of the Internet in Astronomical research

This exhibit will explain the Internet, why it was developed, and how it is used by astronomers. Through computer link to a server, visitors will be able to access World Wide Web astronomy pages.

Exhibit #5 Concept. Achieving a precision surface on the GBT

This exhibit will be a working laser ranging system similar to the prototype used at the GBT test site. The exhibit will consist of a laser, a reflector mounted on a moving surface and an oscilloscope which displays data from the return laser beam. Visitors will be able to change the distance of the reflector and watch the corresponding change on the oscilloscope display. This exhibit will be accompanied by an simple exhibit for younger visitors consisting of optical lasers, mirrors and lenses. The lasers will be mounted above a source of mist so that the beams can be seen.

Exhibit #6. Concept: Exploring interference and its effect on GBT design

This will be an interactive exhibit in which visitors can see and hear different kinds of interference. Examples such as ignition noise, radio stations, transponders, and satellite transmissions will be used. A spectrum analyzer will display the interference graphically. The GBT's offset design will be described as a response to interference problems.

Exhibit #7. Concept: Problems and solutions in GBT design.

This exhibit will explore problems engineers encountered as they took the GBT from concept to completed design. This exhibit will show how Finite Element Analysis was used to test each design for stress.

Exhibit #8. Concept: How does radio astronomy technology affect me?

This exhibit will be a wall chart which shows the web-like relationships linking technology, science, and the citizen. The Green Bank Telescope will be used as an example. Technology developed at the NRAO to measure the surface of the GBT improves on methods for commercial surveying. Sensitive amplifiers developed for use in radio astronomy are adapted for commercial receivers.

Outcome: visitors realize that basic research can have practical applications