Decoding Radio Messages from Space

Transcription

1 I7 Decoding Radio Messages from Space Activity I7 Grade Level: 7 12 Source: This activity is one part of a longer sequence written by Dennis Schatz, and eventually published as part of the original Universe at Your Fingertips and in Astro Adventures by the Pacific Science Center. This particular version was adapted for the Family ASTRO project at the Astronomical Society of the Pacific: and is copyright 2003 by the Astronomical Society of the Pacific. What s This Activity About? When astronomers and linguists think about communicating with extra-terrestrial civilizations, they know words in English are very unlikely to be useful. Much more likely is that we and they can use pictures, just as we do when we are teaching young children to read. The process is likely to involve sending waves at the speed of light and then finding a way to translate the information in those waves into pictures, just as your television set does. What Will Students Do? Students will get familiar with the process of how we might exchange messages with other civilizations in space by using sounds in an audio file to make a picture. Tips and Suggestions Although this activity is written for families, each family member does the sound into pictures translation on his or her own. So this adapts very easily to classroom use. The audio files for this activity can be found in Section 6 (Images, Videos and Sound Files) on The Universe at Your Fingertips DVD-ROM. You may want to copy the file to a CD or your own portable player if you can t play a DVD-ROM in your classroom. This activity could be preceded by I6 Message to the Universe and followed by I8 Translating an Alien Message What Will Students Learn? Concepts Communicating with extraterrestrial civilizations Messages Sound and light Inquiry Skills Communicating Describing Recording Comparing Reasoning Big Ideas Patterns of change Energy Page 1

2 Decoding Radio Messages from Space by Dennis Schatz (Pacific Science Center) An Activity for the Whole Family from Project ASTRO 2003, Project ASTRO, Astronomical Society of the Pacific, 390 Ashton Ave., San Francisco, CA Type of Activity: Facilitated Set up Time: 5 minutes Time to Do: 25 minutes What s This Activity About? To understand the challenge involved in transmitting and decoding a radio message, families listen to a simple sound pattern, convert it into a picture, and then try to interpret the message it contains. Materials Included CD of five audio tracks, or messages (each with simple high and low tones) Master of Decoding Radio Messages from Space worksheet Materials You ll Need to Get Copies of Decoding Radio Messages from Space worksheet (one per person) One marker for each person CD Player Special Note: If a CD player is not available, you can tap out the messages yourself, but it will take a bit of practice! Choose two very different sounding objects to tap on, like a glass (instruct participants to make a mark when they hear this sound) and a block of wood (instruct participants to leave the square blank when they hear this sound.) It may be simpler for you to follow the pattern on the grids if you write it out using the names or initials of the two things you are tapping (i.e. G W G G G G, G W G W G W, G G G W G W, G W G G G G, W W W W W W). Setting up the Activity It is a good idea to review the background information on SETI in the Resources section at the end of this Leaders Guide before beginning this activity. Test the CD player to make sure the audio tracks work correctly and that the volume is adjusted adequately for all of the families to hear the message. Get familiar with the different tracks. Track 1 is a preview of the two tones with five tones of each. Track 2 is a message that spells out, in block letters, the word HI. Track 3 results in a smiley face pattern. Tracks 4 and 5 repeat the HI and smiley face messages, respectively, but at a faster tempo. Use these if your families are really in tune with this activity (i.e., more musically inclined and/or dexterous). Pass out copies of the worksheet to each family member. Note: Unlike most of the other activities in this event, each person does this one separately. Page 2

3 Suggestions for Introducing the Activity Explain how spacecraft travel at relatively slow speeds compared to light. The fastest spaceship humanity has built so far would take roughly 80,000 years to get to the closest star besides the Sun. If we really want to get our message out into space quickly, it would be best to send it as a message traveling at the speed of light. For many reasons, astronomers have concluded that radio waves would be best for sending messages among the stars. Just as television on Earth is just radio waves that are encoded with information to make a picture, so we assume other civilizations might find ways to send pictures using radio waves. In this activity we will investigate a relatively simple way to build up a picture one dot or pixel at a time. A pixel is the smallest element of a picture, like a dot in a newspaper illustration. One kind of code that is easy to transmit is an on-off code. For example, one kind of sound might tell you to make one kind of mark, and another sound would tell you to leave the next part of the picture blank. Use the first track of the CD to have families gain experience at receiving a message from space in the form of two sounds. There are five examples of each sound recorded as a test on the first track (Track 1). Play this just to introduce the two sounds; they don t need to write anything. Tell them what will happen next (before they start). As they listen to the next tracks, they need to fill in or leave blank the grids on their worksheets one square at a time. They should start at the top left most square in each grid and proceed across from left to right. When they get to the end of a row in any particular grid, they should move down to the next row below the last and keep going, again from left to right. When they hear the high tone sound (like an elevator bell) they should make a mark in a square on their grid; when they hear the other, low tone sound (like a drum), they should leave the square blank. The sounds are a bit quick, so families need to settle down and listen. If they think they missed a note (or a mark), tell them to just keep going. There are two sets of grids because many families get lost along the way and so families should be given a second chance to listen to the whole message, if needed. If you repeat the activity, be sure to use the slower paced audio tracks (Tracks 2 and 3). Doing the Activity This is an individual activity, not a cooperative one, so hand out copies of the Decoding Radio Message from Space worksheet to each family member, plus markers to make dots. Let them know it takes too long to make an X or other such mark. Later on, if they wish, they can fill in the marked boxes better. Note: At testing events, the idea of leaving squares blank has been confusing to some people; so make it clear that each square represents a note. Which note they hear determines if they leave the square blank or put a mark in it. Page 3

4 Now transmit a new message as if it were a message from space, by playing Track 2 on the CD (or Track 4, if you think they can handle the quicker pace). Challenge the participants to figure out what the message says. (It is a 6 by 4 grid with the word HI in it.) Key: After taking a number of suggestions about what the message says, reveal the answer. Now, discuss the idea of resolution with the group. Resolution in astronomy means how fine the detail is in the image. For example, if a picture is built up out of many hundreds of dots, it is sharper and clearer than if it is built up out of only dozens or a few hundred dots. The HI message is a low-resolution image and can contain only a limited amount of information. An alien civilization might send a very powerful low-resolution message to attract attention from far away. But it may add to it a higher resolution message that might require better equipment to pick up. Presumably, any civilization discovering the first message will be intrigued enough to build better radio telescopes to find out more. Also discuss how sending letters works when one human is communicating with another, but ask if they think an alien would understand the HI message? Send a new message by playing Track 3 on the CD (or Track 5, if you think they can handle the quicker pace). This one has higher resolution (12 X 10 grid). Have families guess what the message says as soon as they have enough data to be confident in their answer. (It s the smiley face.) Ask them how this message is similar to or different from the first one. Would this one work better as a greeting to aliens? Would they recognize a smiley face as friendly, or would they even have a concept of a smiley face at all? Key: If some families feel that neither message would make sense to aliens who are truly alien, allow them to express this feeling. It is the perfect lead-in to the last activity, where families design their own message. Page 4

5 Family Handout Decoding Radio Messages from Space 2003, Project ASTRO, Astronomical Society of the Pacific, 390 Ashton Ave., San Francisco, CA Use the grids below to decode the messages sent by your event leader. When you hear the high tone sound (like an elevator bell) make a mark in a square on the appropriate grid. When you hear the low tone sound (like a drum) leave squares blank. Begin recording the message in the top left box and move to the right until you reach the end of the row in that grid. Then go to the first box on the left in the next row down in the same grid. Continue this process until the message ends (one grid = one message attempt). Message 1: Attempt 1 Attempt 1 Message 2: Attempt 1 Attempt 2 Page 5