Helioseismology

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SOLAR MUSIC - HELIOSEISMOLOGY

Active Learning Exercises in Planetary
and Solar Astronomy

INTRODUCTION

NEW! Download an Updated Version of this module in PDF format.

This lesson module was written as part of a NASA IDEA grant titled Active Learning Exercises in Planetary and Solar Astronomy for K-3 Students. NOAO astronomers worked with students and teachers of the Satori School in Tucson, AZ, to present eight topics in the elementary classrooms. Each presentation included a discussion with the astronomers and a hands-on, active learning exercise. This module, Solar Music - Helioseismology, encourages the students to realize you can learn about an object by listening to it. Astonomers listen to the Sun's heartbeat to learn about the inside of the Sun.

This module was developed by NSO astronomer Dr. Frank Hill and is intended to be a resource for other astronomers venturing into classrooms. Please contact the NOAO Educational Outreach Office (outreach@noao.edu) if you would like more information about this module or others developed through this program.

OPENING DISCUSSION:

Today we would like to teach you about solar music. The sun is filled with sound, and we can learn about its insides by studying this sound. In fact, this is the ONLY way we can learn about its inside because the light we see from the sun comes only from its outside. This picture shows how the outside of the sun looks to us (show slide #1). But, this picture does not tell us anything about the inside of the sun. Thatís because the picture was made using light that comes only from the outside of the sun. Since the sound is inside the sun underneath the part we can see, we can use sound to learn about the inside of the sun.

Have any of you ever heard the sun? (If they answer "yes", ask them what it sounded like. They may say it sounds like a bird or a rooster, since sunrise generally wakes the birds up. Respond to this answer by saying that the sun causes the birds to wake up and chirp, but that is not solar music.) Whether they answer "yes" or "no" say: I will be playing a recording of solar sound for you in a little while.

Computer image of a slice through the sun showing how sound bounces inside sun

Have any of you heard echoes? Where? (The most likely answer will be "outdoors at a canyon", but ask them if they have heard echoes anywhere else. The answer you are looking for is "inside a room.") Just like sound echoing all around in a room or a concert hall, sound is bouncing all around and echoing inside the sun. Here is a picture created with a computer that shows how sound echoes inside the sun. (show slide #2).

Sound is a vibration, it moves things up and down, back and forth. I have a Slinky™ here, and I need some help to show you how vibrations move things back and forth. (Get a helper to hold down one end of a slinky on a desk top. Take the other end, and shake it horizontally once to get a wave traveling down to and reflecting off the stationary end.) Did you see how the vibration moved the Slinky back and forth? Also, did you see how the vibration bounced off the end that was being held down? The bouncing is what causes echoes, and it also happens inside the sun when the sound hits the surface like in the picture. Also, you can actually see the vibration because it makes the Slinky move.

Computer image of cutaway of sun showing up and down pattern of one solar musical note

The sun is like a huge musical instrument. It rings like a bell, and vibrates like an organ pipe. Does anybody know how many keys or musical notes a piano has? (Answer is 88). Just like a piano has 88 keys or musical notes, the sun has 10 million keys or notes. Astronomers are measuring the solar music in order to determine what its heart is like. This is like listening to a song to understand the singer. Here is a picture made with a computer showing the pattern of up and down movement from a single solar musical note. (show slide #3) The red and blue colors were put into the picture so you can tell which parts of the sun are moving up (blue), and which are going down (red).

Image of actual solar surface showing the up and down pattern
of all 10 million solar musical notes together at one instant

Since the vibrations of the solar sound make parts of the outside of the sun move up and down, astronomers can study the sound by looking at the sun. This is good, since there is no air between the sun and the Earth and so there is no way for us to actually hear the sound. But, we can use special cameras to watch the outside of the sun move up and down. Here is a snapshot of the outside of the sun showing the up and down areas from all 10 million solar musical notes (show slide #4).

This picture (show slide #5) is a way for astronomers to sort out and look at all 10 million notes of the solar music at once. This picture sort of looks like the rainbow pictures you saw earlier, and is really a spectrum of sound rather than light from the sun. You can see a bunch of dots at the left side of this picture. These dots are individual solar notes, like the keys on a piano keyboard. At the right of the picture, the notes blend together and you can't see them very well.

Now, I am going to play an audio cassette of solar sound for you. This cassette was made with a computer using a few of the notes in the last picture I showed you. You can't really dance to it, but it tells us a lot about the inside of the sun.

You can download sound files of the sun from Stanford Solar Center's The Singing Sun.

DEMONSTRATION:

Astronomers can get information about the inside of the sun because different objects have different sounds. The way things are changes how they will sound. I am now going to teach you some of the things we can learn about objects by listening to the sounds they make. I will be using some things called musical triangles.

Here are three musical triangles (Get 3 students at the front to hold up the 3 different size triangles).

What do you notice about them? What is different about them?: They are all different sizes
Which one do you think will make the highest musical note?: The smallest one
Which one do you think will make the lowest musical note?: The largest one
Do you think the musical note of this (middle) triangle will be higher or lower than this (smallest) one?: Lower
Do you think the musical note of this (middle) triangle will be higher or lower than this (largest) one?: Higher

Listen again as I play all three of them in size order (Do it a few times) Now, close your eyes, and listen as I play the three triangles in some order. I want you to listen, and then tell me what size order I played them in (i.e. middle, large, small) Notice that you could tell me what the size of the triangle was just by listening to it without having to see it! The size of the triangle affects how it sounds. In general, large things produce lower musical tones than small things. A chihuahua dog has a higher pitched bark than a St. Bernard.

Next, I will show you how attaching something to the triangle changes the way it sounds. Here is the small triangle again, and here is another small triangle just like this one except I have attached a small clip to it. Here's the sound of the triangle without anything attached. (Strike the small triangle without the clip) Now, here's the sound with the clip attached. (strike the triangle with the clip attached)

How did the two sound different?: The one with the clip attached sounds "dull" or "muffled" compared to the "bright" ringing tone of the unclamped triangle.

The sound has changed because a lot of the tones made by the unclamped triangle have been removed by the clamp. Close your eyes and tell me if I have struck the clamped or the unclamped triangle. Notice that you could tell me if something extra was attached to the triangle just by listening to it.

Finally, I will show you that a spinning triangle sounds different from one that is standing still. Here's the sound of a triangle standing still. (Ring the middle triangle) Now I am going to wind this rubber band up and spin the triangle after I hit it. (Do it but PRACTICE BEFORE THE LESSON!)

What do you notice that is different about the sound?: The spinning triangle will produce a wavering tone whose loudness seems to go up and down.

The sound is different because if something makes a sound while it is moving, it changes the tone of the note heard by someone standing still. You may have noticed that the pitch of a police siren changes as the police car passes you. It's the same thing. Close your eyes and tell me if I am spinning the triangle. Moving things sound different than when they are standing still.

ACTIVITIES:

Bottle Harmonica: Here, the students will construct musical instruments using plastic bottles filled with water. Organize the students into groups of 2 or 3. Distribute the bottles, 1 to each student (2-3 per group). Have the students fill the bottles with various levels of water. Then have them blow across the bottles and ask them what they notice about the sounds that the bottles make. They should notice that when there is more water in the bottle, the pitch of the sound is higher. If they have different size bottles, have them blow across the empty bottles and again ask them what they notice about the sounds. Smaller bottles make higher pitched sounds.

Slinky Vibrations: Have the students experiment with making waves in Slinkies. Stretch a Slinky across a desk, and have one student hold down an end. The other student shakes the free end of the Slinky in various ways to create different wave patterns. Have them first try a single shake so a pulse bounces off the stationary end. Then they can vary the frequency of the shaking to create different harmonics. Ask them to notice how the number of bends in the Slinky changes as they shake the Slinky faster. There will be more bends as they go faster. Be prepared to untangle Slinkies! It is possible to set up a standing wave that seems to remain still.

REVIEW:

Ask the students what they have learned today. Re-emphasize that the sound made by objects tells us something about them. For example, big things (triangles, bottles, dogs) sound lower in pitch than small things. Mention again that the sun is filled with sound, and that astronomers are listening to it to understand what's going on inside it.

REFERENCES:

For further reading you may begin with the following sources:

Browne MW. "Deep solar rumblings may offer key to sun's inner structure." The New York Times, B5, 24-Oct-95.
Leibacher JW, Noyes RW, Toomre J and Ulrich RK. "Helioseismology." Scientific American 253(3):48-57, 1985.
Global Oscillation Network Group (GONG)

Support for this work was provided by NASA through grant number ED-90020.01-94A from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555.

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