Scale of the Solar System


It is difficult to draw a diagram or make a model that accurately represents the vast distances between all planets in our solar system and the Sun. It is equally difficult to represent the size of the planets and the Sun. Using a scale can assist with this, but which scale will be most useful? It is usually not possible to use the same scale for both distance and size as diagrams would not fit on a page and the size of models would not be practical.
Solar System – Distances to scale and planet sizes to a different scale (Image: Wikipedia Commons)

Scales
A scale is a way of reducing a measurement by a defined factor to a more practical or desirable size. For example, it would not be practical to try and navigate using a paper map of a city that did not use a scale to reduce the map to a piece of paper that is easy to read and carry. A scale tells you what distances on the map represent in the real world.
Scales may be written as a ratio of the scaled value to the true value (e.g. 1:100) or shown on maps and diagrams as a bar as shown in the picture below. Scales are not only used for maps but may also be used for diagrams, building plans and models.
Map showing distance scale bar (Image: Wikipedia Commons)

Distance from the Sun
All planets in our solar system orbit the Sun, a star consisting mainly of hydrogen and helium and the source of most heat and light on the planets. The distance a planet is from the Sun, along with a planet’s atmospheric composition, makes a significant contribution to the conditions on the surface of the planet. Earth orbits within what is called the ‘Goldilocks Zone’, being just the right distance from the Sun to allow liquid water to exist on the surface. It’s also not too close to be too hot or overly affected by solar radiation but close enough to gain a suitable level of energy to sustain life within our current atmosphere.
When discussing and comparing the distances planets are from the Sun, the average distance is used as most planets do not have a perfectly circular orbit around the Sun so the distance will change. Kilometres, our standard distance measurement here on Earth are not practical to use when speaking about the solar system as the numbers are so large.
Scientists developed another measurement, called the Astronomical Unit (AU) to make these distances more manageable numbers. One Astronomical Unit (AU) is the average distance between the Sun and the Earth (about 150 million kilometres). Thus, all other distances are compared to the distance between Earth and the Sun. The distances of planets in the solar system are summarised in the table below.
Planet
Average distance from Sun (km)
Average distance from Sun (AU)
Mercury
57,909,175
0.39
Venus
108,208,930
0.72
Earth
149,598,890
1.00
Mars
227,936,640
1.52
Jupiter
778,412,020
5.2
Saturn
1,426,752,400
9.54
Uranus
2,870,972,200
19.2
Neptune
4,498,252,905
30.06

Patterns in the Sky is a PALMS activity that asks students to first calculate the distance between the Sun and planets using Astronomical Units then investigate whether there is a direct relationship between the time taken to complete an orbit of the Sun and the distance between the planet and the Sun. The teacher notes for this activity can be found here and the accompanying student worksheet here.
A fun activity that allows students to observe the vast distances between planets by making a scale model out of toilet paper can be found in this PALMS video. The teacher notes to accompany this activity, Toilet Paper Scale, can be found here and the student worksheet can be found here.

Size of the Sun and planets
When trying to represent the size of the planets and the Sun using a scale, the Sun’s huge size compared to the planets means the smaller planets often end up being so tiny they are difficult to see. For this reason, the Sun is often excluded from diagrams and models or just a portion of it is represented.
Representation of planets to scale (Image: The Conversation)

More information
Some further information on the scale of the solar system and making scale models can be found on the following web pages:


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