Author: Fraser Cain

Everyone seemed to enjoy the answer to my daughter’s question, “what’s the biggest star?”, so I thought I’d give you another insight into space science at the Cain household. A couple of months ago, we built a scaled map of the Solar System. I thought I’d share my process and resources with you, and throw in a few cute pictures of the kids. So come on, let’s build a solar system scale model in your neighborhood. And for those who might be interested, we also put up links of amazing Solar System collectibles from Amazon.com. Your kids will surely enjoy them!

This project happened when I casually mentioned to Chloe that it might be fun to build a scale model of the solar system. You know, some day, when we had time. Chloe and Logan thought it was a great idea, and even though there was half a metre of snow on the ground, it had to happen… right now!

We decided that we wanted to put the Sun in Chloe’s room, and then put all the planets to scale, so that we could walk to Chloe’s school (about a kilometer away), and have all the planets fit nicely – we even included Pluto (which will always be a planet in our hearts).

I found a great calculator that lets you calculate various scale model versions of the Solar System. You put in the size for the Sun and then it calculates both the diameters of the scale model versions of the planets, as well as the scale distances.

We were really fortunate. A version of the Solar System scale model that fit within the distance from our house to Chloe’s school allowed for a Sun that could be cut out of a single sheet of printer paper. I used a protractor to measure out the circle for the Sun, and then cut it out. While the kids were colouring it yellow, I made tiny versions of all planets.

Here are the sizes:

Object	Size (mm)	Size(in)
Sun	200	7.8
Mercury	0.6	0.0275
Venus	1.7	0.0684
Earth	1.8	0.072
Mars	0.9	0.0382
Jupiter	20	0.7892
Saturn	16.7	0.6586
Uranus	6.7	0.2655
Neptune	6.5	0.257
Pluto	0.3	0.012

Then we put our mock planets out into their proper orbits using clear sticky tape. With the Sun just inside Chloe’s room, Mercury was at the top of the stairs. Venus was just outside our front door. Earth at the end of our sidewalk. Mars is on a parking sign across the street from our front door. Jupiter is part way down the next block, stuck to a tree. Saturn is on another tree further down that same block. Neptune is on a parking sign 2 blocks further. Uranus is on a fire hydrant. And finally, tiny Pluto was affixed to a power pole just in front of Chloe’s school.

If you want to get really clever, you can even put in tiny moons. For example, you could put in the moons of Pluto: Charon, Nix and Hydra.

Here are the kids with Mars. Look closer, it’s there.

Here are all the distances:

Object	Distance (m)	Distance (feet)
Sun	0	0
Mercury	8	27
Venus	15	51
Earth	21	71
Mars	32	107
Jupiter	111	367
Saturn	205	673
Uranus	412	1353
Neptune	647	2121
Pluto	850	2787

I was fairly careful measuring distances for the inner planets. But then I just made a rough estimate of my stride length, and used that to mark off the longer distances. Here’s a link to a stride length calculator.

It’s scary to think that a version of Alpha Centauri at this scale would still be 5804.4 km (3606.7 miles) away. That would require a road trip across Canada.

And, now, every day that I walk Chloe to school, we follow the route of our miniature Solar System, and think about just how big the place really is. Even though it’s been a few months since we made our model, most of the planets are still there (we lost Saturn a few weeks back, but we’ll replace it).

Have you built a Solar System scale model for a school project? Let me know how it went and send pictures. Maybe I’ll do a follow up with some more astronomy project ideas.

For extra credit, get your kids to model some of the recently discovered extrasolar planets. Here’s a page that lists their sizes and distances from their parent stars. With so many hot jupiters out there, you could fill a wall with scale versions.

If your kids want to learn more about the Solar System, listen to Astronomy Cast. We did a special tour through each of the planets in the Solar System. Start your tour here with Mercury, then Venus, Earth, Mars, the Asteroid Belt, Jupiter, Jupiter’s Moons, Saturn, Saturn’s Moons, Uranus, Neptune, Pluto, and then the outer reaches of the Solar System.

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The Solar System consists of the Sun, and everything bound to it by gravity. This includes the 8 planets and their moons, the asteroids, the dwarf planets, all the Kuiper belt objects, the meteoroids, comets and interplanetary dust. Since the gravitational effects of the Sun are thought to reach out almost 2 light-years away – almost half the distance to the next star – there could be any number of objects out there, as part of the Solar System.

There are separate regions in the Solar System. First, there’s the Sun, of course. Then there are the inner terrestrial planets: Mercury, Venus, Earth, and Mars. Then comes the asteroid belt; although, not all the asteroids are located in this region. The largest dwarf planet, Ceres, is located in the asteroid belt. Then come the outer gas giants: Jupiter, Saturn, Uranus, and Neptune. Then comes the Kuiper Belt, which includes 3 more dwarf planets: Pluto, Makemake, and Eris. Beyond the Kuiper Belt is thought to be the Oort Cloud, which could extend out to a distance of 100,000 astronomical units (1 AU is the distance from the Sun to the Earth).

Between the planets are smaller objects which never formed a planet or moon. This can range from microscopic dust, up to asteroids hundreds of kilometers across. Beyond the orbit of Neptune, much of this material is icy.

The solar wind emanating from the Sun blasts through the Solar System, interacting with the planets, and pushing material out into interstellar space. The region where this solar wind blows is called the heliosphere, and where it stops is called the heliopause.

The immediate neighborhood around the Solar System is known as the Local Interstellar Cloud. It has high-temperature plasma that suggests that there were nearby supernovae.

The closest star to the Solar System is the triple star system Alpha Centauri.

Are you wondering how many planets there are in the Solar System, or what is the biggest planet in the Solar System?

One of the best pages about the Solar System is the Nine Planets, and Kids Astronomy has more info for kids.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

Where did the Solar System come from? How did we go from space to a star with planets orbiting around it? Before we can look at the formation of the Solar System, we have to see what this region looked like.

Throughout the Milky Way, there are clouds of cold gas and dust, just sitting there, doing nothing. At some point in the distant past, this cloud was disturbed; either through the collision of another galaxy, or the explosion of a massive star.

The explosion would have sent waves through space that squeezed the gas and dust together. The clumping material was able to attract more material with its gravity, and started to collect into the solar nebula. The mutual movement of all the atoms in the cloud gave the solar nebula a direction to spin.

The Sun formed out of the largest collection of mass at the center of the solar nebula. Because it was spinning quickly, the rest of the nebula collected into a flattened disk around the newborn Sun – astronomers call this an accretion disk. Within the accretion disk, additional clumps gathered together; these would eventually form the planets.

The planets started out as tiny specks of dust that clumped together. As they continued to gather together, they became pebbles, rocks, boulders and eventually planetoids. These planetoids violently collided together to become the planets we know today.

By studying the decay of radioactive elements in meteorites, astronomers have been able to determine that the Solar System formed about 4.6 billion years ago.

When astronomers look out into the Universe, they see other Solar Systems forming at different stages. Some are large clouds of cold dust, others are starting to collapse. Others have accretion disks, and some might even have planets clearing out paths in the dust of the disk. We can’t see the formation of our own Solar System, but we can see it happening everywhere we look, so we assume our Solar System formed in the same way.

Here’s an article from Universe Today about planetary formation, and another about how the gas giants might have formed quickly.

Here’s an article from Wikipedia about the formation of the Solar System, and a link to NASA’s Solar System Simulator.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

The hottest place in the Solar System is the Sun, obviously. And the hottest part of the Sun is its core. The surface of the Sun is a mere 5,800 Kelvin, while the center of the Sun is around 15 million Kelvin. That’s hot.

Although the surface of the Sun is relatively cool, the corona can get much hotter. This is the region just above the surface of the Sun, where flares and coronal mass ejections come from. Temperatures in this region can get upwards of 2 million Kelvin.

Okay, outside of the Sun, the hottest place in the Solar System is the core of Jupiter. Once again, while the cloud tops of Jupiter are more than 100 degrees below zero, the core of the planet could be up to 30,000 Kelvin. This high temperature comes from the intense pressure that comes from the entire mass of the planet bearing down on the core and compressing it.

What’s the hottest surface in the Solar System? That would have to be the surface of Venus, which is always an average temperature of 461 °C. In fact, Venus is even hotter than the planet Mercury when it’s in the Sun. Noontime temperatures on the surface of Mercury only get up to 426 °C.

Here’s an article from Universe Today about the hottest place on Earth, and more about the Sun.

Here’s more information about the Sun, and just how hot Venus is.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

Pluto used to be the smallest planet, but it’s not a planet any more. That makes Mercury the smallest planet in the Solar System. The second smallest planet in the Solar System is Mars, measuring 6792 km across.

With all the focus and exploration of Mars, you’d think it’s a really big planet, but actually it’s pretty small. Mars has only 53% the diameter of Earth, and about 1/10th the mass. It only has 15% the volume of Earth. In other words, you could fit 6 planets the size of Mars into Earth, and still have room to spare.

Since Mars is relatively small compared to Earth, and it has a fraction of our planet’s mass, the force of gravity on Mars is very low. If you could walk on the surface of Mars, you would experience only 38% the force of gravity you feel pulling you down on Earth. In other words, if you weighed 100 kg on Earth, you’d feel like you only weighed 38 kg on Mars.

Mars is so small that its core cooled down billions of years ago, and so it doesn’t have a magnetic field any more. Earth’s magnetic field helps push away the Sun’s solar wind, which is trying to carry away our atmosphere. When you match this with its very low amount of gravity, and Mars has lost almost all its atmosphere. The pressure of the atmosphere on Mars is 1% what we experience on Earth.

Here’s an article that explains why Pluto isn’t a planet any more. And here’s the smallest planet in the Solar System.

Want more information? Here’s another article about the biggest planet in the Solar System, and the smallest planet in the Solar System.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

The biggest planet in the Solar System is Jupiter. But the title for the second biggest planet in our Solar System goes to Saturn.

Just for a comparison, Jupiter measures 142,984 km across its equator. Saturn for comparison is only 120,536. So Jupiter is only 1.18 times as big of Saturn. Saturn is big, but it has a much lower mass. Once again, Jupiter is 3.34 times as massive as Saturn.

Since Saturn is so big, but has so little mass, it has a very low density. In fact, if you had a pool big enough, Saturn would float. The density of Saturn is less than water. And this means that you wouldn’t experience a lot of gravity if you tried to walk on the “surface of Saturn”. If you were standing on the surface of Saturn (I know, that’s impossible), you would experience only 91% the force of Earth’s gravity.

If you wanted to compare Saturn to Earth, it’s 9.4 times as big as the Earth, and 95 times as massive. It it was just a hollow shell, you could pack 763 Earths inside Saturn, with a little room to spare.

Wanna see Jupiter? Here are amazing telescopes from Amazon.com which you can buy at reasonable prices:

Here’s the article about how Jupiter is the biggest planet. And here’s another article about just how big planets can get.

If you’d like more info on Saturn, check out Hubblesite’s News Releases about Saturn, and another page on Saturn from NASA’s Solar System Exploration Guide.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

Saturn is easily the most beautiful planet in the Solar System. To celebrate this natural wonder, lets look at some beautiful pics of Saturn.

But if you want to see Saturn by yourself, you can check out these cool telescopes that will help you see the beauty of planet Saturn.

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Let’s start with one of the most beautiful photos of Saturn ever taken. This image of Saturn was taken by NASA’s Cassini spacecraft when it was behind Saturn. In other words, the Sun is completely obscured by Saturn, and illuminating it from behind. The tiny speck in the upper, left-hand side of Saturn’s rings is our own home planet Earth.

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This is a picture of Saturn taken by the ground-based Keck telescope, located atop Mauna Kea in Hawaii. It’s one of the most powerful telescopes on Earth. The Saturn photo was taken in infrared, and shows the strange hot spot located at Saturn’s south pole.

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It’s not the best picture, but you’re looking at one of the first ever images of Saturn captured up close by NASA’s Pioneer 11. During its mission, Pioneer 11 passed just 20,000 km above the cloud tops of Saturn, and captured the first close-up images of Saturn.

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This is an example of a beautiful picture of Saturn taken by NASA’s Voyager 1 spacecraft in 1980. As you can see, the quality has improved significantly over the image captured by Pioneer 11. Both Voyager 1 and Voyager 2 made quick flybys of Saturn and then sped off into space. When Voyager 1 completed its flyby of Saturn, it sped off into the depths of space, while Voyager 2 went on to visit Uranus and Neptune as part of its Grand Tour of the Solar System.

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Here’s another image of Saturn captured by NASA’s Cassini spacecraft. This photograph was taken in May 2004, when Cassini had almost arrived at Saturn. The spacecraft spent another 4 years orbiting Saturn as part of its primary mission, and at the time of this writing, it’s still going strong.

We have written many articles about Saturn for Universe Today. Here are some facts about Saturn.