Solar System Explorer

How to use it

There are four views. Pick one with the buttons at the top of the tool. In every view you can tap a world to open its card, which shows how wide it is, how far it is from the Sun, how long its day and year are, how many moons it has, its gravity and its temperature.

• Sizes. The Sun and all the planets are drawn with their true sizes compared with each other. Scroll sideways to see them all. The Sun is 109 times as wide as Earth, so it is far too big for the page: you only see the edge of it.
• Distances. A long strip shows how far each planet is from the Sun, with every distance true to scale. The line in the middle says You are here and tells you your distance from the Sun, in AU and in kilometres, as you scroll. Tap Send a ray of sunlight to watch light race out from the Sun. One second on the screen is 15 minutes of real time.
• Your weight. Type your weight in kilograms, or tap a quick choice. The list shows what a bathroom scale would say on each world. The Moon is in the list too, just for fun.
• Shrink it. Pretend the Sun is a beach ball, 50 centimetres across. Every world shrinks by the same amount, so you can see how big each planet would be and how long you would walk to reach it. You can switch to a soccer ball or a big gym ball.

Pluto is in every view, but it is labelled dwarf planet, because that is what it is. There are eight planets.

Why it works

Numbers such as 149,600,000 are hard to picture. A scale model turns them into something you can see. When every size in the picture is multiplied by the same amount, the pictures keep the true proportions. That is why Jupiter looks so huge next to Earth, and why Mercury and Pluto look so tiny. On the Sizes strip, Earth is the yardstick: Jupiter is more than 11 Earths wide, and Mercury is a little more than a third of one.

The sizes and the distances need two different pictures, because they cannot fit on the same page. With the planets at their true sizes, the planets would be too small to see on a strip as long as the distances need. In the Shrink it view they share a scale, and that is where you find out how empty space is. With the Sun a beach ball, Earth is about the size of a peppercorn, 54 m away. Pluto is 2.1 km out.

Astronomers measure distances inside the Solar System in astronomical units (AU). One AU is the average distance from Earth to the Sun, about 149.6 million kilometres. Pluto is about 39.5 AU away. Light travels at about 300,000 kilometres every second, so sunlight takes about 8 minutes and 19 seconds to reach Earth, and about 5 hours and 28 minutes to reach Pluto.

Mass is how much stuff you are made of, and it stays the same everywhere. Weight is how hard gravity pulls on that stuff. Gravity at the surface of a world depends on how much mass the world has and how far you are from its centre. Jupiter has so much mass that its pull is about 2.4 times Earth's, so a scale would read about 2.4 times as much. Mars has less than half of Earth's gravity at the surface, about 0.38 times, so the scale would read about 38 per cent. Our explainer What is gravity? says more.

A day here means the time from one noon to the next, and a year means one trip around the Sun. On Mercury a day is longer than a year. In 2006 the International Astronomical Union decided that a planet must orbit the Sun, be round, and have cleared the space around its orbit of other objects of a similar size. Pluto has not, so it became a dwarf planet.

Every number in the tool was copied from NASA's Planetary Fact Sheet (nssdc.gsfc.nasa.gov/planetary/factsheet) on 12 October 2026. The tool works out everything else itself, from those numbers: the weights, the scale models, the AU and the times for sunlight. The number of moons keeps changing, because astronomers are still finding new ones, so the counts are NASA's list on that day. The planets are friendly drawings, not photographs.

For parents and teachers

The Solar System Explorer is written for Years 3 to 8. Younger children enjoy the sideways scroll and the weight list. Older students can work with the AU, the light travel times and the scale model, and can check the maths with a calculator.

Ideas to try:

• Make the model for real. Use a soccer ball for the Sun and walk out along the school oval, using the distances in the Shrink it view. Peg a seed or a peppercorn for each planet.
• Ask: Why would a spacecraft take so long to reach Neptune? Use the Distances strip and the light times to talk about how far away it is.
• Weigh a class. Each child types their weight and writes down what they would weigh on Mars. Then ask what stayed the same, and why.
• Find out which planet has the shortest day and which has the longest year, and compare the cards.
• Look up how many moons Jupiter has this week, and see if NASA's number has changed since the tool was written.

The tool does not claim more than it knows. The colours and the surface patterns are drawings, the Sun is shown only at its edge, and the dots on the Distances strip are not to scale. The Moon in the weight list is not a planet, and the gas giants have no solid ground, so their weights are for floating at the cloud tops.

The tool works with touch, mouse and keyboard. Press Tab to reach a world and press Enter to open its card. If your device is set to reduce motion, the ray of sunlight is switched off, and a list tells you how long sunlight takes to reach each world instead. The tool saves nothing at all on your device, not even the weight you type, and sends nothing anywhere.