Step 3: Making the Journey
If you skipped Part 1, then you need to know know that in this activity, you will build a scale model of the Solar System as far as Pluto. You will use familiar objects and easy, approximate measurementsâmostly simply pacing off distances. This is not a project about being extremely precise; the goal is to develop a strong perception of just how big the solar system is and how small the planets are within that system.
For preparation, you need only to assemble the collection of properly-sized objects listed in the requirements table (See Step 2) and print out the âcheat sheetâ youâll carry on the Walk. A glance at a map of your local area will help you decide which way to take your expedition and to identify some landmarks to stand in for more-distant things like the far edge of the Oort Cloud. To build your own interest and enjoy some discoveries of your own, check out some of the links Iâll include in the references section (Step 4).
You can feel free to substitute alternate model planets, using the scaled sizes as a guide; however, most of the items called for can be found in an average family home, borrowed from classroom parents, or purchased at a very modest outlay. While modern kids may not find the contents of kitchen spice jars terribly fascinating, using an allspice or peppercorn seed as your âEarthâ model will give them a lifelong reference point–theyâll be smelling pumpkin pie or watching a chef grind pepper and that spark of memory will remind them of this project.
Because the scaled planets range from the size of a pin point to the size of a jacks ball, it also makes sense to attach each object to something larger, such as an inverted cup or a 4 by 6 index card. If you have access to sports equipment, the bright-colored cones often used for laying out a temporary playing field are helpful. You can position the planet-holder and also tape a âPlease Leave Our Experiment Hereâ sign to the top of the cone. And the bright colors and signs help the explorers to look back and spot the distant planets. Again, be creative! There is no need to run out and buy sports equipmentâany handy rock or a brick will do to keep your objects and notes in place.
Here’s my Walk kit, ready to go.
When reviewing the Cheat Sheet, youâll see that this model describes our solar system as far as the outer edge of the Oort Cloud. However, to go all the way to the Oort Cloud in this model is a journey of 75 miles (100 km), so donât expect to travel that far. Instead, as part of your preparation, identify a few local landmarks 1 or 2 miles from your start point and also pick some regional and further-off destinations to match the scaled distances for such key locales as the Oort Cloud, the heliopause, the estimated positions of the Pioneer and Voyager spacecraft, the far edge of the Kuiper belt, and our further neighbors in the Universe. If youâre too short on time, the Cheat Sheet includes some general destinations, but your own localized ones will be much more meaningful to the group. If your group wonât have time to walk all the way to Pluto, find out where Pluto would be in that locale and point ahead to that location before you do turn back.
Once in the classroom, before launching your exploratory mission, start with a quick review of the concept of scale. Regardless of your target age group, toys which are also scale models of cars or airplanes or trains are helpful examples. Quickly walk through a sample of numerical proportions to give a sense of how it goes when you are creating your own scale model: for instance, sketch on the board or a sheet of poster paper a rough scale drawing of the classroom room at 1 inch per foot (5 cm per m). Rather than slowing down the project with extra work, prepare for this session by making your own rough measurements of the classroom dimensions in advanceâsimply pace off the length and width and note any additional features to the room. Remember, the idea is to illustrate your point, not to create an architectural drawing.
Moving on to the Solar System, start with the SunâŚan 8-inch-diameter playground ball or an ordinary soccer ball fits our scale. Ask if anyone can guess what size the Earth should be to go with this âSunâ. The guesses are very likely to be way off, because most âmodelsâ used in classrooms and the pictures in the textbooks are not at all to scale. In those, Earth is shown as a recognizable ball appearing as much as a tenth the size of the Sun.
Once you have a few guesses on record, share the key data. Write on the board or a flip chart as you go, to keep the presentation lively. (Nothing kills attention like a PowerPoint!) The Sunâs diameter is about 800,000 miles (1400 thousand km), and weâre using an 8-inch (18 cm) ball, so each inch stands for 100,000 miles (or, a cm stands for 75,000 km). The Earthâs diameter is only 8,000 miles (12,700 km). So how big will the model Earth be? It turns out we need something less than 1/10th of an inch across, only 0.08 inches (0.17 cm). So now you can pass around your âEarthââŚa peppercorn will work, so will an allspice seed. (And, yes, you can get away with crumbling up a bit of paper and claiming itâs a spitwad you found.) If you have a spice-jar worth of seeds, everyone can have their own Earth to keep. Let the students take a moment to actually compare the sizes of Earth and Sun. Itâs a dramatic difference, nothing like what their textbooks show.
Now itâs time to figure out where the Earth and Sun should be to fit in with this scale. Start by inviting students to guessâŚthey will likely assume you can fit the Earth-Sun model easily inside the room. So now, add the distance data they need and we can âstepâ through the necessary calculation:
- The Earth is roughly 93 million miles (150 million km) from the sun.
- In our scale model, thatâs 930 inches (2000 cm)
- or 78 feet (20 m),
- or 39 steps of about 2 feet (40 steps of 0.5 m)
Notes:
- In our model weâre using a pace distance reasonably close to the average womanâs step length and not too far off the step length of a child who is supposed to be walking but canât resist running. If your group is adult men or tall women, you can use the worksheet to adjust the number of steps accordingly.
- Our scale in SI (Système international, or metric) is slightly different than in English units, so that those using the SI version can also use simple round figures.
At this point, try to keep a straight face while pretending to start building the model inside the classroom. Dramatically place the âSunâ at one end of the room and try to pace off 39 or 40 steps. Unless youâre doing this activity in a large lecture hall or a cafeteria, you will quickly run out of space (pun intended). By now, it should be clear to the students that this is to be an outdoor activity.
If the group is not too insanely anxious to get outdoors, you can take one more minute to assemble a part of the model which will fit in the roomâthe Earth-Moon system. Our Moon is nearly Âź the diameter of Earth, so itâs actually an important body in its own right. And itâs close by. In our scale model, the Moonâwhich can be represented by a single nonpareil or cake âdĂŠcorâ candyâis 2 3/8â or 5 cm from Earthâso Earth & Moon can be stuck to a card or piece of paper. Keep in mind that if your group is too anxious to get outside, you can choose to save this step for your arrival at the Earthâs position in the model outside.
Earth and Moon are stuck together
Set the very few ground rules for the mission plan. The model is built by counting stepsâthe students will be the ones to do the counting and you (the project leader) will expect them to try hard and in return will not be too fussy about precision or how the measurement accuracy may be affected when leadership shifts from short to tall students.  The group will remain cohesive, so no-one misses out on any important discoveriesâand no one will charge ahead lest they get âlost in spaceâ. And everyone should understand the time constraints.
When the group is large, Iâve had success assigning small subgroups to accompany one adult leader as the âvanguardâ to each planet, leaving the rest behind until they have âlanded,â then allowing the followers to run full-speed to catch up. If you do this, itâs important to ensure everyone has a turn to be in the vanguard at least once. If the students have been studying the planets, the vanguard students can also be asked to provide just a few key bits of information to the other explorers as features they have âdiscoveredâ about the planet they just reached. However, resist the urge to turn each stop into a seminarâthe goal is to travel as far as possible across the system quickly enough to return before class time ends.
Remind the group that itâs a long walk across the solar system and then get started for real. Carry your Sun to a central location outside. If you can park Sol near a tall landmark (such as a flagpole), youâll find it easier to point back to the âcenter of the Solar Systemâ as you move further away. Take your Cheat Sheet in hand (the page from the resource kit listing your step-off distances) and read out the number of steps from the sun to Mercury. Send the Mercury explorer team ahead to place Mercury in its position, and quickly join them with the rest of the group. If the vanguard has some cool facts to share about Mercury, give them time to speak. And move on to Venus and the rest of the inner planets.
The asteroid belt portion is the first region containing many objects. If you pause at Ceres, the biggest dwarf planet in the inner Solar System, it helps reduce the stigma of Pluto being âonlyâ a dwarf planet. The fun part in these âbeltâ regions is to pretend to dodge the small asteroids or other objectsâwhile you may mention that there really isnât any significant risk of running into an asteroid, that is no reason to turn down the chance to pretend youâre in a crowded mess of obstacles just like in the movies. Even Neil deGrasse Tyson, in his reboot of Cosmos, includes a sequence in which his Ship of the Imagination zigs and zags through, first, a crowded Asteroid Belt and later a densely-packed Oort Cloud.
If time is short or you are working with younger children, it is reasonable to make it to Jupiter (donât forget to dodge the asteroids on the way out) point out roughly where the outer planets, Pluto, and the further objects would be found and then head back to Earth.
In any case, carry some ordinary first-aid supplies and be sure to have extra adults on hand to slow down those who want to jump to lightspeed. Donât worry if you donât have a straight route to useâŚtwisting and turning your way around the streets of a neighborhood is equally impressive. If time will permit, participants can bring lunches and picnic in the Kuiper Belt before returning. And remember, as you return to collect the planet models, it is just as fun to rediscover the distances on the way back.
