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Copyright 1989 by Guy Ottewell
Universal Workshop
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This is a classic exercise for visualizing just how BIG our Solar System really is. Both the relative size and spacing of the planets are demonstrated in this outdoor exercise, using a mere peppercorn to represent the size of the Earth. Guy Ottewell has kindly given permission for this electronic presentation of The Thousand-Yard Model; his exercise is presented in its original form, indexed with a few anchors to help you find you way around the large file. We also include a catalog describing several Ottewell publications. Image of the planets courtesy ofNASA.
Can you picture the dimensions of the solar system?
Probably not, for they are of an order so amazing that it is difficult either to realize or to show them.
You may have seen a diagram of the Sun and planets, in a book. Or you may have seen a revolving model of the kind called an orrery (because the first was built for an Earl of Orrery in 1715). But even the largest of such models--such as those that cover the ceilings of the Hayden Planetarium in New York and the Morehead Planetarium at Chapel Hill-are far too small. They omit the three outermost planets, yet still cannot show the remaining ones far enough apart.
The fact is that the planets are mighty small and the distancesbetween them are almost ridiculously large. To make any representationwhose scale is true for the planets sizes and distances, we must gooutdoors.
The following exercise could be called a Model, a Walk or a Happening. I have done it more than twenty times with groups of varied ages (oncewe were televised) or with a single friend; and others, such as elementary-school teachers, have carried it out with these instructions.Since it is simple, it may seem suitable for children only. It can,indeed, be done with children down to the age of seven. Yet it can alsobe done with a class consisting of professors of astronomy. It will notwaste their time. They will discover that what they thought they knew,they now apprehend. To take another extreme, the most uncontrollablehigh-school students or the most blase college students unfailingly switchon their full attention after the first few paces of the excursion.
There is one other party that may profitably take the planet-walk, andthat is yourself, alone. Reading the following description is nosubstitute: you must go out and take the steps and look at the distances,if the awe is to set in.
First, collect the objects you need. They are:
Sun-any ball, diameter 8.00 inches
Mercury-a pinhead, diameter 0.03 inch
Venus-a peppercorn, diameter 0.08 inch
Earth-a second peppercorn
Mars-a second pinhead
Jupiter-a chestnut or a pecan, diameter 0.90 inch
Saturn-a hazelnut or an acorn, diameter 0.70 inch
Uranus-a peanut or coffeebean, diameter 0.30 inch
Neptune-a second peanut or coffeebean
Pluto- a third pinhead (or smaller, since Pluto is the smallest planet)
You may suspect it is easier to search out pebbles of the right sizes. But the advantage of distinct objects such as peanuts is that their rough sizes are remembered along with them. It does not matter if the peanut is not exactly .3 inch long; nor that it is not spherical.
A standard bowling ball happens to be just 8 inches wide, and makes a nicemassive Sun, so I couldn't resist putting it in the picture. But it may notbe easy to find and certainly isn't easy to carry around. There are plenty ofinflatable balls which are near enough in size.
The three pins must be stuck through pieces of card, otherwise their heads will be virtually invisible. If you like, you can fasten the other planets onto labeled cards too.
Begin by spilling the objects out on a table and setting them in a row. Here is the moment to remind everyone of the number of planets -9- and their order--MVEMJSUNP. (This mvemonic could be made slightly more pronounceable by inserting the asteroids in their place between Mars and Jupiter: MVEMAJSUNP.)
The first astonishment is the contrast between the great round looming Sun and the tiny planets. (And note a proof of the difference between reading and seeing: if it were not for the picture, the figures such as "8 inches" and ".08 inch" would create little impression.) Look at the second peppercorn--our "huge" Earth--up beside the truly huge curve of the Sun.
Having set out the objects with which the model is to be made, the nextthing is to ask:"How much space do we need to make it?"Children may think that the table-top will suffice, or a fraction of it,or merely moving the objects apart a little. Adults think in terms of theroom or a fraction of the room, or perhaps the corridor outside.
To arrive at the answer, we have to introduce scale.
This peppercorn is the Earth we live on.
The Earth is eight thousand miles wide! The peppercorn is eight hundredths of an inch wide. What about the Sun? It is eighthundred thousand miles wide. The ball representing it is eight inches wide. So, one inch in the model represents a hundred thousand miles in reality.
This means that one yard (36 inches) represents 3,600,000 miles. Take a pace: this distance across the floor is an enormous space-journey called "three million six hundred thousand miles."
Now, what is the distance between the Earth and the Sun? It is 93 millionmiles. In the model, this will be 26 yards.
This still may not mean much till you get one of the class to start at theside of the room and take 26 paces. He comes up against the opposite wall atabout 15!
Clearly, it will be necessary to go outside.
Hand the Sun and the planets to members of theclass, making sure that each knows the name of the object he or she iscarrying, so as to be able to produce it when called upon.
You can make some play with the assigning of the objects to the "gods" who are to be their bearers. Selecting a blond Sun, a hyperactiveMercury, a comely Venus, a redhaired or pugnacious Mars, a ponderous orregal Jupiter, a ring- wearing Saturn a blue-eyed Uranus, aswimming-champion Neptune, a far-out Pluto can enliven the proceedings andteach a few scraps of mytholgy or planetology. It is unfortunate thatonly Venus and Earth (the Moon) are female (most of the goddesses havegiven their names to asteroids instead).
You will have found in advance a spot from which you can walkathousand yards in something like a straight line. This may notbe easy. Straightness of the course is not essential; nor do you have tobe able to see one end of it from the other. You may have to "fold" itback on itself. It should be a unit that will make a good storyafterwards like "All the way from the flagpole to the Japanese garden!"
Put theSun ball down, and march away as follows.(After the first few planets, you will want to appoint someone else to dothe actual pacing-call this person the "Spacecraft" or "Pacecraft"-so thatyou are free to talk.)
10 paces. Call out "Mercury, where are you?" and have the Mercury-bearer put down his card and pinhead, weighting them with a pebble if necessary.
Another 9 paces.Venus puts down her peppercorn.
Another 7 paces.Earth
Already the thing seems beyond belief. Mercury is supposed to be so close to the Sun that it is merely a scorched rock, and we never see it except in the Sun's glare at dawn or dusk-yet here it is, utterly lost in space! As for the Earth, who can believe that the Sun could warm us if we are that far from it?
The correctness of the scale can be proved to skeptics (of a certain maturity)on the spot. The apparent size of the Sun ball, 26 paces away, is now the sameas that of the real Sun-half a degree or arc, or half the width of your littlefinger held at arm's length. (If both the size of an object and its distancehave been scaled down by the same factor, then the angle it subtends must remain the same.)
Another 14 paces.Mars
Now come the gasps, at the first substantially larger leap:
Another 95 paces toJupiter
Here is the "giant planet"-but it is a chestnut, more than a city block fromits nearest neighbor in space!
From now on, amazement itself cannot keep pace, as the intervals growextravagantly:
Another 112 paces.Saturn
Another 249 paces.Uranus
Another 281 paces.Neptune
Another 242 paces.Pluto
You have marched more than half a mile!(The distance in the model adds up to 1,019 paces. A mile is 1,760yards.)
To do this, to look back toward the Sun ball, which is no longer visible even with binoculars, and to look down at the pinhead Pluto, is to feel the terrifying wonder of space.
That is the outline of the Thousand-Yard Model. But be warned that if you do it once you may be asked to do it again. Children are fascinated by it enough to recount it to other children; they write "stories" which get printed in the school paper; teachers from other schools call you up and ask you to demonstrate it.
So the outline can bear variation and elaboration. There are differentthings you can remark on during the pacings from one planet to the next,and there are extra pieces of information that can easily be grafted on. These lead forward, in fact, to the wider reaches of the universe, andmake the planet walk a convenient introduction to a course in astronomy. But omit them if you are dealing with children young enough to beconfused, or if you yourself would prefer to avoid mental vertigo.
I recommend that you stop reading at this point, carry out the walk once, and then read the further notes.
While you are talking and introducing the idea of the model, it may behelpful (depending on the age of the audience) to build up on a blackboardsomething like this:
realin modelEarth's width8,000 miles8/100 inchSun's width800,000 miles8 inchestherefore scale is100,000 miles1 inchtherefore3,600,000 miles36 inches or 1 yardand Sun-Earth distance93,000,000 miles26 yards
Having come to the end of the walk, you may turn your class around andretrace your steps. Re-counting the numbers gives a second chance tolearn them, and looking for the little objects re-emphasizes how lost theyare in space.
It works well, in this sense: everyone pays attention to the last fewcounts- "240...241...242"-wondering whether Neptune will come into view. But it does not work well if the peanut cannot be found, which is all toolikely; so you should, if you plan to do this, place the objects on cards,or set markers beside them (large stones, or flags such as the pennantsused on bicycles).
Also, the Sun ball perhaps cannot be left by itself at the beginning ofthe walk-it might be carried off by a covetous person if not by thewind-so send someone back for it when the walk has progressed as far asMars.
(I once, having no eight-inch ball, made a colored paper icosahedron,and had to give chase for afar when I saw someone appropriating it. Onthe return from another walk, I met a man holding his mouth while hisworried companion said "Did you bite it?"-incredibly, he had picked up oneof the peppercorns! The other edible planets are, of course, prey forpassers-by. Hazards like these may be regarded as our model'scounterparts of such cosmic menaces as supernovae and black holes.)
On each card, the child who recovers it may write briefly the placewhere it was-"At 5th Street," "At John Cabonie's house"... Then, back inthe classroom, the objects as kept in a row on a shelf, as a reminder ofthe walk. Or they may be hung on strings from a rafter.
Since pecans, pinheads, peanuts, and especially peppercorns cannotalways be readily found when another demonstration is called for, I keepat least one hand, in one of the small canisters in which 35-millimeterfilm is sold.
Anyone you take on this planet-walk may finish it with a desire to seteyes on the planets themselves. So it is best to be able to do it at adate when you can say: "Look up there after dark and you will see[Jupiter, for instance]."
Thus on the first nights of 1990, when darkness falls, Jupiter will bethe brightest "star" high in the east of the sky, and Venus will be thebrightest one setting in the west.
For any other specific times, consult the Astronomical Calendar, themagazines Sky & Telescope or Astronomy, or a local college sciencedepartment, planetarium, or amateur astronomer.
Point out that the nine planets do not stay in a straight line. Theystay about the same distances from the Sun, but circle around it(counterclockwise as seen from the north).
They go around at various speeds. The inner planets not only havesmaller circles to travel but move faster. Thus, Mercury goes around inabout 3 months; the Earth, in a year; and Pluto in about 250 years.
The circling movements mean that the planets spend most of their timemuch farther apart even than they appear in out straight-line model. Thedistance between two planets can be up to the sum of their distances fromthe sun, instead of the difference.
Jupiter and Saturn, for instance, can be as close as 95 paces as in themodel, or up to 382 paces apart at times when they are on opposite sidesof the orbits.This is the case in the years around 1970,1990, and 2010. (Jupiter overtakes Saturn about every 20th year.) Think of the spacecraftPioneer 11, which actually covered this immense distance. Launched fromEarth in April of 1973, it looped around Jupiter in December 1974, andarched back all the way over the solar system, on its way to visit Saturnalso. This journey is so long-the distance back from Jupiter plus theeven greater distance out to Saturn-that the spacecraft did not reachSaturn till September 1979. During the Thousand- Yard walk is thedramatic time to tell people about this, and let them reflect on therefinement with which the spacecraft had to be aimed around the south poleof Jupiter in just such a way that it might five years later drop betweenSaturn (this acorn) and its rings.
Schematic pictures often show the planets on parade at about equaldistances- much as when you first arrayed them on the table. This, as wehave seen is unrealistic: the intervals are very unequal. There arethese features to point out:
So, if you need to foldthe walk back on itself, because of not having space to walk a thousandyards, Uranus is the point at which to turn.
Throughout most of human history, only six planets have been known: Mercury, Venus, Earth, Mars, Jupiter, Saturn. (Most of the time nobodyknew what planets are or that the Earth is a planet.) Then, in the lastthree centuries, three new planets were discovered. Uranus, thoughtheoretically visible to the naked eyer on fine nights if you know justwhere to look, was not noticed till 1718; Neptune was discovered bycareful calculation and search in 1846; and Pluto in a similar way, butnot till 1930 after a quarter of a century of meticulous search, for evenin large telescopes it is lost among countless thousands of equally faintstars.
And anyone who takes our planet-walk will say: "No wonder!"
Pluto not only is smaller than the other eight planets, but is smallerthan the Moon and half a dozen other satellites of planets. It is, as wehave seen, the exception to the rule that the inner planets are small (androcky) and the outer planets large (and gaseous).
It is also exceptional in its orbit, which somewhat messes up our model.
It is true that Pluto's average distance from the Sun is about3,666,000,000 miles (1,019 paces in our model). But its orbit, instead ofbeing nearly circular like those of the other planets, is very eccentricor elliptical: part of it is much nearer in toward the Sun and part muchfarther out. At present Pluto is on the inward part. In fact, it isnearer in than Neptune! This is so from 1979 until 1999, when Pluto willagain cross outward over Neptune's orbit.
Thus a true statement is that Pluto is usually the outermost knownplanet (but for just these ten years out of 250 Neptune is) and that thedistance in our model from the Sun to the outermost planet is about athousand yards on average (but it should really vary from only Neptune's777 yards in these ten years, to as much as 1,275 yards when Pluto is atthe outermost part of it orbit).
The other planets circulate in the same plane as the Earth, at leastnearly enough that we can represent this by the plane of the ground. ButPluto's orbit is inclined to this general plane by the fairly large angleof 17 degrees. This means that part of the huge orbit lies far above(north of) ours and part far below. At present Pluto is still well to thenorth side. So if you want to mention this, you can tell the lastplanet-carrying child to walk 242 paces and then climb a tree-"justkidding..." (Actually the tree should be 200 yards high! And there areparts of the orbit where Pluto should be up an even higher tree or down avery deep hole in the ground.)
When Mars, moving rapidly along its relatively nearby orbit, passes infront of Jupiter or Saturn, and we look at these planets through atelescope, we are surprised to find that the disk of Mars looks much thesmaller. Jupiter looks three times as wide as Mars, though it it eighttimes farther away!
The planet-walk will have impressed you with the great distance fromMars onward to Jupiter, and thus will give this observation its surprisingquality. However, the planet-walk also gives you the means to visualizethe reason. The farther away two objects are, the less the distancebetween them counts, and the more it is a matter of their own actualsizes. Or, put another way, angular size decreases slower and slower withdistance.
When we first laid the row of objects out on the table, there was anextreme contrast between the Sun and the rest. The word "size" is vague,since it could mean width (diameter), volume, or mass (amount of matter). In volume, the Sun is 600 times greater than all the planets put together. As compared with the small but rather dense Earth, the Sun is 109 timesgreater in width; 1,300,00 times greater in volume; and 330,000 timesgreater in mass.
Within the planets themselves, there is quite a contrast betweenJupiter and the rest. Jupiter contains almost three times as much matteras all the other planets together-even though Saturn comes a good secondto it in width.
This is partly because Saturn is the least dense of all the planets (itwould float on water, if there was an ocean big enough). But it is alsoan illust- ration of the difference between the kins of "size." If youmultiply a planet's width by, say, 3, you mutltiply its cross-sectionalarea by 9, and its volume by 27. Thus a relatively small differencebetween the widths of Saturn and Jupiter means a much larger differencebetween their capacity. This, too, is easier to understand when you lookat the solid objects representing them.
The Moon is, on our scale, 2.4 inches from the Earth.
You can, on reaching the position for the Earth, pause and put down aMoon beside it. This Moon will have to be another pinhead (theoreticallybetween the sizes of Mercury and Pluto).
Look down on this distance, the length of your thumb; the greatestdistance that Man has yet leaped from him home planet. Reflect on themanned mission to Mars now being suggested (14 yards in our model) or thetrips proposed in science fiction: to Jupiter as in the film 2001 SpaceOdyssey (109 yards); to the nearest star (four thousand miles in ourmodel); to the Andromeda Galaxy (half a million times farther again).
The planet walk is an antidote to the "scientific" school ofastrologers, who suggest that the planets disturb particles in our bodies. When one can visual- ize how remote these planets are, it is easy tounderstand that the nearest of them, Venus, when nearest to us, has thesame gravitational or tidal effect as a truck 14 miles away, or ahigh-rise building 300 miles away.
During the walk, the immense distances between the planets and the Sunmay make people incredulous that the planets can truly feel thegravitational influence of the Sun at all, let alone be so much in itscontrol that they orbit faith- fully around it forever. After all, if ourmodel is to scale, then this peppercorn, representing the Earth, mustexperience a similar gravitational pull from that far-off ball,representing the Sun. Does it? It certainly shows no inclination to falltoward the ball, and has no need to stave off such a fall by orbittingaround the ball!
The peppercorn does feel the gravitational pull of the ball. Thedifference is that there is so much other matter in the environment of themodel, which is not present in the environment of the things beingmodeled: the sidewalk, the the pillars of the arcade you are walkingalong, the grass and trees, your feet and above all the air pressing downand the total mass of the Earth underneath. These are all so huge that theatraction of the ball, without becoming any less, becomes by comparison anegligible influence in the distance. If there were, in interplanetaryspace, any object corresponding to even one of these things - say, afour-million-mile slab of rock, corresponding to the paving-stone on whichthe peppercorn is lying - then the Sun's influence on the Earth wouldbecome negligible. It is only because space is so empty that the Sun isthe nearest important gravitational influence on the Earth.
The solar system does not really end with Pluto.Besides the planets, there is a thin haze of dust (some of it bunched intocomets). Any of this dust that is nearer to the Sun than to any otherstar may be in the gravitational hold of the Sun and so counts as part ofthe solar system. So the outermost of such dust may be half way to thenearest star.
On the scale of our model, Pluto is a thousand yards or rather morethan a half a mile out. But this true limit of the solar system is twothousand miles out.
A thousand miles, in our mode, is the distance called a light-year (in reality,about six million million miles).
The distance to the nearest star, Proxima Centauri, is 4.2 suchlight-years.
The human mind can never conceive this thing called alight-year, which is the currency of our small-talk aboutthe universe. (It is probable that we cannot directly conceive anydistances above about 600 yards, which is where we sub- consciously placethe horizon). But through the model we move as far toward conceiving itas we ever can.
I, at least, have seemed to have some respect for the term, light-year; and to have some sense of what I mean when I use it-since I made thesensory approach to it through this model.
The rest of the stars in our galaxy are probably on the order of fourto ten light-years apart from each other, as we are from our nearestneighbor.
This is a stunning thought when (having done the Thousand-Yardexercise) you go out at night and look at the Milky Way. It is a haze oflight so delicate that it can no longer be seen from inside ourlight-ridden cities. It consists of the bulk of the stars in our galaxy,piled up in the distance, so numerous and so faint that we cannot see themseparately. Yet they are all the same kind of distance from each other aswe are from the nearest of them. That is to say, if we could hop to anyone of them, cavernous black space would open out around us,and the Sunitself would become part of that same dense far-off wall of stars, theMilky Way!
Most of the stars that populate space are smaller than the Sun, andcertain exotic kinds are smaller than Mercury or the Moon. But others areincredibly larger.
Thus a "giant" star such as Arcturus, about 25 times wider than theSun, would have to be represented in our model by a ball 6 yards across. Rigel, a "super- giant" 50 times wider that the Sun, would be a ball 11yards across-the size of a whole classroom. If we stood it in place ofthe Sun, it would reach most of the way out to the first planet, Mercury. Red supergiants are larger still: Antares, 700 times wider that the Sun,would be about 160 yards across, so that Mercury, Venus, Earth, and Marswould be orbiting deep inside it! Betelgeuse is thought to vary fromabout 550 to 1000 times the width of the Sun, so that if substituted forthe Sun it would be a colossal ball of 260 yards with Jupiter barelyclearing its surface. (One more, the dark companion of the star EpsilonAurigae, used to be regarded as the largest star known, 2800 times widerthan the Sun-large enough to swallow the solar system to well beyondSaturn. But it is more likely some kind of cloud.)
Yet these monsters, like all stars, are so far away that they appear tous as points with no width at all.
(The Sun itself, in its "red giant" phase, will swell up like this andput an end to us-about 4,000,000,000 years from now.)
If you mention these facts during the walk, you are likely to stir upcuriosity as to where these humongous stars can be seen. The AstronomicalCalendar will show where, and also whether they can be seen at all at thenecessary season. Epsilon Aurigae is almost circupolar, so it is visibleat all seasons. It is the top of the little triangle of stars justdown-right from Capella. Here again is an example of how much better itis to have done the Thousand-Yard Walk before anything else. I haveoften, while showing people the sky, drawn their attention to EpsilonAurigae and told them they might be looking at the largest star; it has acertain interest, of course, but it has no such impact as when they havepreviously seen, the Sun Ball and the 247 paces to Saturn.
Globular clusters are awesome balls of up to a million stars, in aspace perhaps 150 light-years across. In photographs such a cluster lookslike a swarm of luminous bees, ever thicker toward the core, which appearsa solid unresolved white. It seems as if the stars must be almosttouching and the space among them must be white hot, burning with light. And in fact these stars are 25,000 times more densely packed than normal. Yet this means that they still average about a tenth of a light-yearapart-in our model a mere hundred miles from each other instead of fourthousand.
Even these densest aggregates of stars are mostly empty space.
Since the discoveries of Rutherford and Bohr about 1911, we havethought of the atom by means of the "planetary model"; a "Sun" (thenucleus) orbited by smaller "planets" (electrons). But there are greatdifferences.
Leaving aside the entirely distinct natures of the bodies and theorbits, there is a difference in relative sizes: the spaces within theatom are even larger a hundred times larger-than the spaces within thesolar system!
The distance from the Sun out to Mercury is about 45 Sun-widths. Butthe distance from the nucleus out to the nearest electron-orbit it on theorder of 5,000 nucleus-widths. (There are nuclei of various sizes.) So,if our model were to represent the atom instead of the solar system, the"Sun" (nucleus) would have to be a ball 100 times smaller (the size of apeppercorn) and the "planets" (electrons) far too small to be visible;either that, or we would have to spread the objects 100 times fartherapart.
Truly, the universe is mostly empty space, with very rarely encounteredstars and planets. Yet even the matter of which those stars andplanets-and people- are made is far emptier space, with far more rarelyencountered particles.
What do you begin an astronomy course with? A firsttaste of the constellations? Celestial co-ordinates? Physics? History? I have found that the point never fails to come, either in these lessonsor in later ones, where I am glad I can say (or wish I could say): "Youremember how in the planet-walk we saw that..."
I conclude that this should be the first lesson, the aperitif, or atmost the second. Tell the students: "Astronomy is an outdoor subject, andeven though it's now daytine" (or, "is cloudy") "we're going right outsidefor our first exercise!" It will wake them up, make them think you are alively teacher, leave them with a sense of expecting future lessons to befun too (so that- don't be alarmed!-they will actually classify the restof the course as fun even if some of it isn't).
Since devising the thousand-yard model, I have learned of similar onesby other people. The idea, after all, is obvious; what is crucial to itsworkability is the choice of scale.
Sir John Herschel, a wonderful scientist and son of Sir WilliiamHerchel who discovered Uranus, proposed in his book Outlines of Astronomy(1849) a model of the solar system using peas, oranges, plums and thelike. The scale he chose was too large, so that from the Sun to Plutowould have been 3 miles.
In the World Book is depicted another model, with the Sun reduced tothe size of a quarter, so that the solar system fits within a baseballstadium. Here the scale is too small: the lesser planets would be almostinvisible, and could not be represented by objects more memorable thanvariously sized grains of sand.
At least one modern education film shows a teacher making a model, witha weather-balloon as the Sun and steel globes of various sizes as theplanets. Here again the objects are not memorable and the scale is toolarge. The Sun and Earth have to be at opposite ends of a football-field;after that the making of the model ends, and we are told that Jupiterwould be 4 more football-fields away, etc.
Any model whose scale is much larger than that of the Thousand-YardModel (such as Herschel's and the film's) results in distances of a mileor more, which people cannot be asked to walk during a lesson. Any modelwhose scale is smaller (such as those of orreries, ceiling models, theWorld Book, and all pictures) results in planets too small to see (unlessthe scale is falsified).
In both cases, therefore, the model remains something to becontemplated only in the head. And it is the real doing and seeing thatare indispensable to the effect.
If, instead of taking people for a walk, you are merely talking tothem, it can be useful to say that if the Sun is shrunk to the size ofyour head, then the Earth will be the size of the pupil of your eye. These have about the same width as the eight-inch ball and the peppercorn.
Light travels 186,283 miles (or 299,793 kilometers) per second. Itcould travel, for instance, 7 1/2 times around the Earth in one second. A"light-year" is the distance light travels in a year, and similarly we cancall the distance light travels in a second a "light second," etc.
in modelMoon to Earth1.28 light-seconds2.4 inchesSun to Earth8.3 light-minutes26 yardsSun to Jupiter43.27 light-minutes132 yardsSun to Pluto5 1/2 light-hours1019 yardsSun to Proxima Centauri4.22 light-years4000 miles
Our scale is 1: 6,336,000,000. This means that:
1 inchrepresents100,000 miles1 foot "1,200,000 "1 yard "3,600.000 "1 mile "6,336,000,000 "928 miles "5,880,000,000,000 miles or light-year
To carry out the exercise with a group, and to be able to answerquestions promptly; you may make a copy of this tabular summary and takeit with you. (Another way, especially if you do the exercise severaltimes, it to memorize the successive numbers of paces-10, 9, 7, 14, 95,112, 249, 281, 242. I do it by means of a private mnemonic with lettersfor numbers, but that is another subject.)
in the modelmiles yards inchesdiameter of Sun 800,000 8.0(ball)distance from Sun to Mercury 36,000,000 10diameter of Mercury 3,000 0.03 (pinhead)distance from orbit of Mercury to Venus 31,000,000 9diameter of Venus 7,500 0.08 (peppercorn)distance from orbit of Venus to Earth 26,000,000 7diameter of Earth 8,000 0.08 (peppercorn)distance from orbit of Earth to Mars 49,000,000 14diameter of Mars 4,000 0.04 (pinhead)distance from orbit of Mars to Jupiter 342,000,000 95diameter of Jupiter90,000 0.90 (chestnut)distance from orbit of Jupiter to Saturn 403,000,000 112diameter of Saturn75,000 0.75 (filbert)distance from orbit of Saturn to Uranus 896,000,000 249diameter of Uranus32,000 0.30 (peanut)distance from orbit of Uranus to Neptune 1,011,000,000 281diameter of Neptune30,000 0.30 (peanut)distance from orbit of Neptune to Pluto 872,000,000 242diameter of Pluto 1,400 0.01 (pinhead)total of distances 3,666,000,000 1,019distance from Earth to Moon 240,000 2.40diameter of Moon 2,000 0.02 (pinhead)
In my earlier versions the total distance in the model happened to comeout at exactly 1,000 yards. This had no real signifcance, but wasconvenient since it made the complete model easy to remember. Unfortunately it was based on some- what incorrect distances for theplanets from Mars outward. Mile orginally meant "thousand paces" (Latinmille passuum) but grew to be 1,760 yards.
One day presumably the metric system will complete its hold on theEnglish speaking countries as it has on most of the others. To me thatwill be a sad day because the lumpish term kilometer can never subsitutefor the fine old monosyllable mile. But, in case this planet-walk isstill in use, it will need a decimal translation.
Our basic unit of the yard will have to be translated into the meter. A yard, in origin a pace (a fairly long one), is 36 inches; a meter, inorigin 1/40,000,000 of the circumference of the Earth, is 39.27 inches, sowe are fairly lucky. The Pacer's legs should stretch a bit more.
For our scale, instead of 1: 6,336,000,000, we'll choose the roundernumber of 1: 6,000,000,000. Thus, in pacing between the planets, 1 meter(pace) represents 6,000,000 kilometers. In the sizes of the bodies, 1centimeter represents 60,000 kilometers.
in the modelkm m cmdiameter of Sun 1,400,000 23 (ball)distance from Sun to Mercury 58,000,000 10diameter of Mercury 5,0000.08 (pinhead)distance from orbit of Merury to Venus 50,000,000 8diameter of Venus12,0000.20 (peppercorn)distance from orbit of Venus to Earth 41,000,000 7diameter of Earth13,0000.20 (peppercorn)distance from orbit of Earth to Mars 78,000,000 13diameter of Mars 7,0000.10 (pinhead)distance from orbit of Mars to Jupiter 550,000,000 92diameter of Jupiter 143,0002.40 (chestnut)distance from orbit of Jupiter to Saturn 649,000,000 108diameter of Saturn120,002.00 (filbert)distance from orbit of Saturn to Uranus 1,443,000,000 240diameter of Uranus51,0000.90 (peanut)distance from orbit of Uranus to Neptune 1,627,000,000 271diameter of Neptune49,0000.80 (peanut)distance from orbit of Neptune to Pluto 1,404,000,000 234diameter of Pluto 2,3000.04 (pinhead)total of distances 5,900,000,000 983distance from Earth to Moon 384,0006.40diameter of Moon 3,5000.06 (pinhead)
This makes the total walk slightly less than a kiloneter (1000 meters). You can call it "about a kilometer." Then a light-year (9,460,530,000,000kilometers) because in the model 1,600 kilometers, and the nearest star,at 4.22 light-years, is about 6,700 kilometers away.
You may learn about other publications by Guy Ottewell in this catalog. Daniel Washburn, working with the NOAO Educational Outreach Office and supported by NASA through the Arizona Space Grant Consortium, contributed greatly to this World Wide Web presentation of theThousand Yard Model.
 | NOAO is operated by theAssociation of Universities for Research in Astronomy(AURA), Inc. under cooperative agreement with theNational Science Foundation. |  |
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