Below, youâll find a handy supply document you can download, with shopping lists for small and large groups and a range of cost estimates, depending on how much of the supplies you can acquire from available supplies or donations by participants.  With a minimal outlay, you and your group can experience being comet chasers–observers of comets.
Basically, you need a bunch of badminton birdies for your comet headsâkeep in mind you donât need performance-grade shuttlecocks or even new ones. If your high school has a badminton team, they will have worn-out birdies you can take off their hands.  A grungy, beat-up birdie makes a more realistic comet head.
Birdies for Comets
And you need a bunch of ribbonâcurling ribbon for the comet tails. The supply sheet estimates ribbon packages at around $8, but if you look at this photo, youâll see the last time I bought supplies, it was out of the clearance bin at $2. And if you can get one in five of your participants to bring in a roll to share, it wonât cost you a dime.
Zoom Out–Yes! Here’s All You Need To Make Comets
The one oddball item is that tulle fabric ribbon for the big comet. This you might have a hard time finding in your junk drawer unless youâve been helping a bride make wedding tchochkes. But for $10 you can buy enough to make three huge comets. Cut five-yard lengths and tie one end of each to a vane of a single birdie, allowing a few inches of extra length to fan out as the cometâs âcomaâ. Tulle scrunches up easily, so even a six-inch-wide ribbon will feed through the holes between the birdieâs vanes.
Detail–How To Tie Fabric Tails
You should be able to borrow a portable fan and a playground or soccer ball. If you canât, it will take a roughly $25 expenditure to get those items in stockâa cost you can recoup in part by either donating it to the group youâre working with or simply deducting the expense as part of your cost of volunteering.
And it is presumed you can find a pencil, which makes holding the small model a little easier when you’re doing the demo with the fan;Â here’s the trick for hooking the pencil to the comet head:
Holder For Fan Experiment
Depending on how good you are at scrounging supplies and locating soccer balls, your costs will range from $10 to $85 for typical group sizes.  The spreadsheet I use has a calculation column to adjust the requirements list for other class sizes So, if you want a copy of this fully-functional workbook, âlikeâ the Facebook page & Iâll send you one via a Facebook âmessageâ. (You can also try emailing me through the âcontactsâ page here, but youâll get a faster response on FB.) Your FB contact will be used for nothing other than sending you a file and boosting the “likes”-count on my page. [Insert maniacal laughter, if desired.]
Meanwhile, you can get the static workbook as a pdf right away:
Now that you are all excited about comets, here are some fun places to go where you can find more cometary material:
A lovely one-page summary from the Spaceguard Program (sponsored by the European Space Agency) gives a clear description of comet tail structureand dynamics, including a neat animation of what both tails look like as the comet proceeds around the sun. The ion tail streams straight back, while the dust tail is curved a bit as the particles within the dust tail blend movement due to their individual orbits about the sun and the forces of the radiation pressure. Net, both tails roughly point away from the sun, as in our demonstration.
Check out NASAâs solar system photo gallery, with images from NASA and European Space Agency exploration missions and telescopes.
Visit the Lunar and Planetary Instituteâs educational site, with even more hands-on activities for young astrophysicists. Roam their site for educator workshops and more.
OK, seriously, I’m not the only science blogger keen on comets.
Our guy Euler was the first one to suggest that light exerts pressure, but we had to wait over 100 years to get to Maxwell, who proved it, and then another quarter-century went by before some Russians managed to measure radiation pressure. (Also, gotta love Google Books.)
Oh, and by 1915 the proof of radiation pressure made it into Scientific American.
OK, we’re back for part 2. Remember that our goal is to impart an intuitive, long-term understanding of how comet tails work. Iâll give you an observation worksheet that students can use during the Comet Running game, but if time or attention-spans are too short for a worksheet, dispense with that element in favor of learning through movement and Socratic dialogue. (What? You think an engineer wouldnât have read the Greek philosophers?)
If you have time and enough outdoor space for the âGameâ version of this simulation, move right along to “Stage 2” now. The promise of a chance to make their own models is what will entice the students back to the classroom. Otherwise, save the great outdoor model for another time or place and move directly to “Stage 3,” building the individual models.
Stage 2: The Game
That’s One Big Comet
This is an outdoor game, and it works to best advantage with a nice BIG comet model. Four five-yard lengths of white fabric streamers attached to a single badminton shuttlecock (âbirdieâ) make our Comet Chase model. A playground ball or a soccer ball (around 8â in diameter) stands for the sun.  Sort the participants into groups of no more than five and no fewer than three, and move to the great outdoors. A grassy area is safest, because this game involves some complicated running; if youâre stuck with pavement, tone down the running to âjoggingâ and allow a little extra time.
Start by laying out the ground rules for the game. First, each group will get to play every role. There are three parts: being the sun, being the comet, and being observers back on Earth. Remind everyone of your local rules for behavior outside. Itâs harder to listen to instructions out in the sunshine and fresh air!
Take a moment to review the lesson so far. Place the model Sun on the ground, at least ten yards away. Ask an adult helper or one of the students to stand about halfway between the class and the Sun and to hold the head of the comet
Large Comet Head With Coma
while you extend the tailâs long white streamers.  This model is much more evocative of the scale of a real comet, which has a tail tremendously longer than the diameter of its coma, or headâbut itâs still not a scale model. Allow for some oohs and aahs, but move on to your query: which direction should the cometâs tail point? Donât move yet; both you and your helper just stand in place.
Large Comet: Incoming or Outbound?
Donât be concerned if it takes more than one answer to get the right one! Some may still want to know which way your comet is moving. But in a few moments, you should achieve the consensus that the tail should point towards the class and away from the sun.
Now, add the movement and ask everyone to call out which way for you to move. Ask your helper to start walking (slowly, please!) towards the sun and then to loop around the sun. You will need to move quickly to keep the cometâs tail pointing away from the sun. In fact, even if your helper cooperates by walking slowly, you will need to break into a run! As you run, if the students arenât already hollering directions to you, tel them to keep reminding you which way to point the tail: away from the Sun!
Pause partway and while you catch your breath you can demo a technique for helping to align the tail while in motion. With your outside hand, hold the streamers. With your inside hand, point at the Sun. The tail-runners should always find that pointing at the Sun also means pointing at the cometâs head.
Now, it is finally the studentsâ turn. Run as many iterations as necessary to ensure that each group does each job at least once. For instance, for a class of 20, allow time to run the game at least four times.
The Comet Group: The comet group needs one Head and up to four Tail-Runners. Name the comet after the person whoâs serving as the Head. Comets are always named according to the last name of the cometâs discoverer. So if you have Robin Williams as the cometâs head, then this will be Comet Williams. Getting the comet named after him/her may compensate for the fact that the âheadâ only gets to walk slowly around the sun.
Meanwhile, the tail-runners get to hold the ends of the tail streamers and run to keep the cometâs head between themselves and the Sun. In the normal course, the âtailâ group will tend to lag a little and spread out, but that actually serves to more-accurately represent the shape of the dust tail. If youâre working with a two-tails group, designate one especially determined runner to represent the ion tail by taking one ribbon and maintaining a straight line from the ribbon end through the comet head to the sun.
The Sun Group: The sun group stands in the middle of your running space. One or two group members hold the model sun overhead. This makes it easier for the Comet group to see if they have successfully aligned the comet head and the sun. If the tail-runners stray out of line, members of the sun group need to to shout out âGot you! Got you!â or “Solar Wind Coming!” to warn them that the solar forces are blasting the tail.
The Astronomer Group: The people who are not part of the sun-comet demonstration still have a critical role. They are not just watching other people play the game, but they are tracking the shape of the cometâs tail as it passes around the sun, as observers on Earth. Depending on their perspective at each point in the cometâs orbit, the tail will appear longer or shorter. For example, if the comet is roughly between Earth and the Sun, the tail may look short, because it is stretched towards us. If you have time for writing, ask the Observers to sketch the comet as they see it. (See the handout.) In an average class, each student will get to observe the comet at least twice, which is very helpful for catching the unexpected views.
When every group has had a chance to play every role, take a few minutes to review one more time. As a comet is orbiting around the sun, which way does its tail point? By now, everyone should be willing to state that the tail always points away from the sun.
Still, you may still have a few hold-outs who are not quite sure this can be true. If you are lucky and itâs a sunny day, you have a hole card to play. Invite the students to each imagine that they are comets. âGuess what? You can see exactly where your tail would be. Who can point at it? Whereâs your tail, Comet Human?â
If you are not saved by the insight of a student whoâs totally absorbed the lesson, it is OK to resort to hints. âEveryone has one. Itâs easy to see. Yes, you can see your comet tail! Where is it? Which way does a cometâs tail point? Right: away from the sun. Whereâs the sun right now? What do you have thatâs pointing away from the sun? Itâs not bright and shiny like a cometâs tail. Itâs dark, because there are no sunbeams there.
âYes! Your shadow is your comet tail. It points away from the sun, always, no matter what direction you run.â
Stage 3: The Reward
Finally, everyone needs a model comet of their own to take home and show off and share with family members everything about how comet tails work. This is not an art project; itâs an opportunity to review and experiment individually. If some students are fussy about carefully arranging their streamers to make a colorful pattern, that is all right, but the point is to assemble a working model.
Each participant needs 24 feet of curling ribbon and a birdie (remember what I told you earlier about calling it by its proper nameâbe prepared for lots of giggling and teasing if you insist on that) . Cut the ribbon into eight lengths of roughly 3 feet. It is perfectly all rightâand in fact more realisticâif the streamers come out various lengths. And depending on the studentsâ social skills, it is also all right for them to exchange colors once the cutting is done. (There are always some who prefer to discover a multi-color comet and others who prefer monotone.)
Once each student has six streamers, have them tie one end of each streamer to the head of the birdie.
Detail–Attaching Ribbon For Comet Tail
Your meticulous planners will distribute them evenly around the netting; others will be clumped randomly. Either is fine. Every comet is unique and most are quite non-uniform.
Be real. This project is not done when it the comets have been only built. Everyone needs a chance to try them out. They will, of course, want to toss them around the classroom; if this is not acceptable, make some provision for them to try out that technique outdoors. More scientific, of course, as time permits, is to allow the participants to take turns trying out their comets in the pretend âsolar windâ of the classroom fan. As long as they willing and able to mind safety rules about working around a fan, by all means have everyone try out the tail position approaching, passing, and retreating from the Fan Sun. But donât get all hot under the collar if other comets are flying through the room while you monitor the fan users. Just imagine youâre in the Oort Cloud and youâll be OK.
Up next:Â Supplies You Need and Resources You Can Use
In this activity, the most importantidea is to explore and experiment with models and games to understand how a cometâs tail behaves as the comet hurtles around the sun. The key concept is that the cometâs tail is being pushed away from the sun by the ionizing radiation, solar wind and even the light itself blasting out of the sun. This means that when the comet is inbound, approaching the sun, its tail streams behind it, like a horseâs tail. But on the outbound journey, as the comet leaves the sun behind, its tail flies out in front of it. What we hope the participants will take away from these activities is a picture of what a comet looks like as it moves and the knowledge of why it looks that way.
Comet-tail behavior simply makes sense when âexperiencedâ from the cometâs point of view. If by any chance some of these facts are a discovery for you, too, donât feel like you have to keep it a secret that you are learning–have fun with it. A key ingredient in the formula for growing a scientist is that finding out how the universe works is fun. Or, in the words of one physicist profiled in the film Particle Fever: The real answer to âwhy do we do this is . . . because itâs cool.â)
Keep in mind the constraints of your particular situation when assembling your materials and pre-planning the project. For instance, if there arenât enough classroom scissors or if session time is tightly constrained, you can pre-cut the ribbon for the individual comet models into 3-foot lengths. Be aware of opportunities for participants with special needsâfor instance, the comet-running activity does require at least one person to be standing still. In return, that one who just canât stand still could be a pinch-runner. If the group as a whole isnât particularly fast-moving, the ârunningâ game can be done at whatever pace suits the team.  (One can be a âstudentâ at any ageâmost of us middle-aged folks are not exactly speed-demons.) If you’re planning this as a home-schooling project, this is one you’ll want to save for a get-together with other home-schoolers–you need at least three players and it is ever so much more fun with a group.
Stage 1: The Small-Scale Experiment
This description may look long, but that’s just to let you walk through it easily and to share some photos to help. This whole Stage 1 should take about fifteen minutes, tops.  I’ll spare your weary eyes and park the “Stage 2” and “Stage 3” activities in the next posting–but don’t worry, the entire activity fits into a single science session if you can claim an hour’s time to play with.
Before distributing materials, bring out one individual model comet, the sample to be used for the models everyone will take home. Itâs simply an ordinary badminton birdie with long streamers of ribbon tied to it. For now, keep the ribbons bunched up inside the net of the birdie. Explain that the ball at the end of the birdie is the cometâs nucleus, the frilly part can be its atmosphere, or coma, which begins to form as the gas and dust which jets away from the outer layers comet as it warms up.
One Small Comet
Notes: Iâd suggest that you relax and let your sample comet be imperfectâcomets are messy creatures by nature and you donât need that one super-meticulous individual slowing down the whole event by striving to exactly matching a perfect sample. If you have an older, more experienced group of comet enthusiasts to work with, you can interject the extra information about the distinction between the ion and dust tailsâperhaps even represent them by different ribbon colors.On the other hand, if youâre working with anyone between the ages of 5 and 15, and you donât want to deal with distracting snickers and giggles erupting through the group, simply refrain from using the technical term for a birdie. Oh, come on, you know why.
OK, back to it. The ribbon represents those gases and dust particles that make up the cometâs tail(s). Now, if we toss our model across the room, what happens to the streamers tied to it? Right . . . they float out behind. They donât stretch out in front or clump in a bunch around the head of the âbirdieâ. You can demonstrate by trying to throw your comet backwards: hold the tail in front and toss, but the tail will just fall back to the head andâif your throw is a mighty oneâend up in back again..
Now, invite answers to a key question: why does the ribbon float behind? What pushes the tail behind the cone as it flies through the room? With a little nudging, you should get general agreement that it is the air pushing on the lightweight streamers, shoving them behind the âheadâ of our comet.
But now we must turn to a more difficult line of questioning. Pull out playground or soccer ball (a handy model for the sun), and ask one student to stand and hold up your Sun so everyone can see the next portion. Bunch up the cometâs tail in the back of the shuttlecock again, and carry the comet in a âflightâ around the âSunâ. As you move, ask the students to think hard about what happens to the cometâs tail as it whips around the sun.
Start easy. Shake out the streamers, and stretch them out with your free hand. Move the comet towards the sun. Which way should I point the streamers? Everyone will be quick to tell you to pull them backwards, away from the sun. Now, place the comet at its closest approach to the sun, just before it curves back to head into deep space again. âIâm at the Sun now,â you can say, âzooming around the back of it. And moving as fast as Iâll go in this journey. Which way should the streamers point?â
Usually this question generates some disagreement. A reasonable argument would be that you should hold the streamers behind the comet, as it moves, which would mean the cometâs tail would point along a tangent to its orbit around the Sun. (Even if the students are covering tangents in math, please donât interrupt yourself to pause and discuss tangents right now! Use this lesson later to enliven the math session.)
Tail Behind?
Tail In Front?
Tail Sideways?
Some students may suggestâquite logically–that when you are that close, the Sunâs gravity should pull the tail towards it. If the group is large enough, you should also get someone who can argue that the tail should point away from the sunâfor now, it doesnât matter if this is a knowledge-based claim or just a contrarian viewpoint from snarkiest person in the room. Whatever hypotheses are offered, just accept them as proposed solutions and demonstrate what each would look like.
Finally, move to the âoutboundâ portion of your cometâs orbit. âOur comet now flies on away from the sun, perhaps to return in another century or two. Now, which way should the cometâs tail point?â Again, if you have managed to keep a poker face so far, the most popular answer is likely have the tail streaming behind the comet. As before, accept and demonstrate each of the guesses. If students have reasons for their theories, let everyone hear them. Discussing and justifying hypotheses is an integral part of the real scientific process.
If you have access to a blackboard (oh, well, itâs modern times, so, okayokayokay, you can use your smelly whiteboard or that fancy tablet-linked projector), now is the moment to leave off demonstrating with the model and sketch the competing hypotheses for everyone to see. Your picture will look kind of like this. Please remember to Keep It Messy.
Discussing Possible Tail Directions
Have you ever read one of those annoying mystery stories in which the author leaves you in the dark about a critical fact that solves the entire case? Well, here too, we have denied our puzzle-solvers an important clue. So, tell the group itâs time for a change of topic. But actually what weâre doing is rolling out the narrative twist that makes the whole thing so cool.
Here on Earth, it is air that pushes the streamers on our comet model. But how much air is there out in space? (So little that you might as well say âzeroâ!) But without air, why should any comet have a tail at all?
What comes out of the sun? You should hear the following answers: heat, light, maybe even radiation. But has anyone heard of the solar wind? The sun blasts out particles, too? The sun is shooting out plasma, protons and electrons flying through the solar system at thousands of miles per hour. This is the solar wind, which blows through the solar system all the time, at thousands of miles per hour. The particles are tiny, not even as big as atoms, so it is an invisible wind. And like wind, itâs not perfectly even, it gusts and changes from moment to moment as the Sun itself changes.
All of those things we named help to make our comets look the way they do. Consider your audienceâŚ
Explanation #1: You are all correct. All of that stuff blasting out of the sun–light, radiation, heat, and the solar wind–shove all that stuff leaking out of the comet into a tail. And since all that stuff is coming from the sun, the only way the tail can point is away from the sun.
Explanation #2: All of those answers are correct . . . and they all combine to make a cometâs tail. The heat of the sun warms the comet to free the gases and dust. The solar wind blasts the gasesâand the particles in the solar wind also interact with those gases, stripping some of their electrons to make that part of the tail a glowing stream of ionized gas. The radiation from the sun actually can push things, and that pressure is just strong enough to shove those tiny dust particles enough to counteract their tendency to fall towards the sun. And the visible sunlight reflects from the spread-out cloud of dust, making the comet shine in our night sky.
Again, with older/experienced participants, now is the time to clue them in that radiation pressureâthe totally cool idea that sunlight itself exerts pressureâexists because light is electromagnetic radiation and electromagnetic radiation is a wave and a wave [http://physics.info/em-waves/] pushes on the objects it encounters. You may not feel battered and bruised by the TV and radio waves powering through you day and night or be physically bowled over by the sunlight forming a gorgeous rainbow. But: itâs enough to push fine grains of dust. The only sad thing about radiation pressure is itâs not common knowledge yetâitâs been proven since 1873.
To represent these solar forces, we need to make a breeze. For that job, a fan does the trick. When we turn it on, it blasts a healthy âsolarâ wind. (Be sure to experiment in advance with your fan and sample comet–there’s a lot of variation in fan settings.)
Inbound Comet
Hold the comet in the âinboundâ position, with the front of the birdie pointed at the Fan Sun. Yes! We were all correct: the tail points behind the comet as it moves towards the sun.
If the fan is strong enough, you can also use the model to hint at how the length of the cometâs tail changes. Far from the sun, the comet has no tail; far from the fan, our streamers dangle to the floor. A little closer in, a real comet’s tail appears as a pale streak behind it; as you approach your fan, the model’s streamers lift up and begin to flutter weakly behind it. Near the sun, the tail stretches out millions of miles behind a real cometâs head; near the fan, the your streamers stretch their full length.
Now, what about when the comet is heading away from the sun? Which way will the tail be pointing, now that we know about the solar “wind”? Nearly everyone will see, now, that it must point away from the sun.
Outbound Comet
Demonstrate that this works: you point the birdieâs nose away from the fan, turn on the blast, and the streamers flow out over the front of the birdie. The shape of the birdie helps emphasize the incongruity of our expectationâthat the tail goes behindâwith the reality: the solar forces push the tail.
If the class has patience for one more test, add the third question: what happens when the comet is rounding the far side of the sun, and is pointed âsidewaysâ? Hold the comet model perpendicular to the flow of the fan.
Comet At Perihelion
Let everyone see how the tail sweeps out to the side of the comet. It always points away from the sun, no matter what direction the comet is pointing.