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Visualizing the True Sizes in Our Solar System
🎨 What you will need:
A pencil, some paper, and an eraser. These will be for taking notes and helping you in the activities.
A ruler for making measurements.
(Optional):
Coloured pencils for personalized art work.
Calculator for calculating planetary size ratios.
📐 What is a Planet's Diameter?
📐 What is a Planet's Diameter?
Welcome to the Lab!
Traditional textbooks compress space maps to fit on a flat page, making planets look uniform. That is a total optical illusion! Planets drastically change in sizes and we will look at those differences here, starting with understanding how we measure the widths of planets using diameters.
Space is three-dimensional, but to measure how wide planets are, astronomers treat them as flat, two-dimensional circles. A diameter is a straight line that cuts directly through the exact centre point of a circle, touching both outer edges. It tells us the true width of a planet’s face.
🧠 Think About It: If you sliced a gum-ball ball perfectly in half, the flat edge left behind forms a circle. The widest point across that flat circle is its diameter!
🌎 Establishing Our Cosmic Baseline
🌎 Establishing Our Cosmic Baseline
To see true size comparisons of the other planets to ours, we will introduce an Earth Unit (EU).
We will identify 1.0 EU as the representation of the true diameter of a single Earth.
The other 7 planet will be stacked and measured against our home planet's diameter using this value (1.0 Earth Unit).
Friendly Reminder: Don't forget to take notes!
Understanding the Earth Unit:
To see how big 1.0 Earth Unit actually is you can click the button below or navigate to 'The Earth Unit (EU)' tab located at the top of the page.
Brain Kickstart Challenge:
Attempt to answer the question and record your answer on your paper. Then click the question below to reveal the answer and check your work.
How many Earth's diameter's does it take to make 1.0 EU?
How many Earth's diameter's does it take to make 1.0 EU?
1.0 EU is based on Earth's diameter; therefore, it takes 1 Earth diameter to make 1.0 EU.
Did you get it right?
Make sure to be honest with your marking because monitoring your progression will only make you better.
🔍 Try it yourself: The Search for Diameters
🔍 Try it yourself: The Search for Diameters
The Mission:
Look around your room right now. Any circular object—a clock, a water bottle cap, or a coin—has a diameter.
You can measure it correctly using your ruler, but remember that it must pass straight through the dead centre. If your line skips the centre point, your size calculations will be completely wrong!
You'll notice the vast variety of diameters there are from object to object, this diameter variation is not just limited to planets.
The Other Planet Diameters
The Other Planet Diameters
Now that we have established a general unit of measurement to compare to the other planets (the EU), lets start looking at these comparisons.
We will start these comparisons by working from the 3 closest planets to our Sun (Earth not included) and working our way out to the 4 furthest planets.
Fun Fact: The 4 outer planets in our Solar System all are bigger than Earth.
The 1st Planet from our Sun
The first planet from our Sun is actually smaller than Earth.
It's diameter is almost two fifths of Earth's diameter (⅖ EU), therefore it takes about 2 and a half of this planet's diameters to make 1.0 EU.
Do you know which planet this is? Record your answer down then click this text box to check.
Mercury!! Did you get it right?
Mercury is the smallest planet in our Solar System and is closest to our Sun.
As you can see by the image above, it takes an estimated 2 and a half Mercury diameters to make 1.0 EU.
The 2nd Planet from our Sun
The second planet from our Sun is almost the same size as Earth, just slightly smaller.
It's diameter is a little over nine tenths of Earth's diameter (⁹⁄₁₀ EU), therefore we only need 1 of this planet's diameters to make a close enough estimate to 1.0 EU.
Do you know which planet this is? Record your answer down then click this text box to check.
It's Venus!! Is this what you wrote down?
Venus is very similar in size to Earth and the second planet from our Sun; Earth is the third.
As you can see by the image above, Venus's diameter is very similar to Earths and is basically 1.0 EU by itself.
The 4th Planet from our Sun
The fourth planet from our Sun is Earth's closest planetary neighbour and is the most researched planet in our Solar System other than Earth. This planet is also the most visited planet in our Solar System.
It's diameter is a little bigger than one half of Earth's diameter (½ EU), therefore it only takes a little less than 2 of this planet's diameters to make 1.0 EU.
Do you know which planet this is? Record your answer down then click this text box to check.
It is none other than the famous Mars!! Were you correct?
Mars is the closest planet in our Solar System to Earth and is the subject of many Sci-Fi movies and lore. It is also the last of our Solar System's 4 inner planets.
As you can see by the image above, it takes a little less than 2 Mars diameters to make 1.0 EU.
The 5th Planet from our Sun
The fifth planet from our Sun is the biggest in our Solar System.
It's diameter is almost a staggering 11 Earth diameters (11.0 EU), therefore 1 of this planet's diameters makes almost 11.0 EU!!!
Do you know which planet this is? Record your answer down then click this text box to check.
The massive Jupiter!!! Did you get this correct?
Jupiter is the largest planet in our Solar System and its diameter is almost a whopping eleven times bigger than Earth's diameter!
As you can see by the image above, 1 Jupiter diameter is basically 11.0 EU.
The 6th Planet from our Sun
The sixth planet from our Sun is the second largest planet in our Solar System. It's most famously known for the giant rings wrapping around it.
It's diameter is a little over nine times Earth's diameter (9.0 EU), therefore 1 of this planet's diameters makes over 9.0 EU.
Do you know which planet this is? Record your answer down then click this text box to check.
Saturn!! Is this what you wrote down?
Saturn is in second place for the biggest planet in our Solar System, losing only to Jupiter. If you factor in Saturn's rings, they stretch out to be an enormous 2 Jupiter diameters wide!
As you can see by the image above, 1 Saturn diameter is a little over 9.0 EU.
The 7th Planet from our Sun
The seventh planet from our Sun is the coldest in our Solar System despite not being the furthest from our Sun. It is also one of the bluer planets but sometimes confused for being a distinct blue, when in reality it is closer to a really light shade of blue; almost whitish.
Do you know which planet this is? Is it bigger or smaller than 1.0 EU? Record your answers down then click this text box to check.
It is the planet Uranus and it's diameter is almost a full 4 Earth's diameters (4.0 EU), therefore 1 of this planet's diameters almost makes 4.0 EU.
Were your answers correct?
Uranus is the third largest planet in our Solar System and is almost the furthest from our Sun.
As you can see by the image above, 1 Uranus diameter is almost 4.0 EU.
The 8th Planet from our Sun
The eighth planet from our Sun is also the furthest in our Solar System. It's diameter is just slightly smaller than Uranus's diameter (4.0 EU), therefore 1 of this planet's diameters also almost makes 4.0 EU.
Do you know which planet this is? Record your answer down then click this text box to check.
The last planet in our Solar System, Neptune!! Did you get this one right?
Neptune is the fourth largest planet in our Solar System and is really close in size with Uranus. However, Neptune is a more distinct shade of blue in comparison to Uranus.
As you can see by the image above, Neptune and Uranus are similar in size and both almost 4.0 EU.
Understanding the Earth Unit Ratios:
To see how the Earth Unit (EU) measurements were obtained you can click the button below or navigate to the 'Cosmic Measurment Chart' tab located at the top of the page.
Test Your Knowledge
Test Your Knowledge
Now that we have covered all the planets in our Solar System, it's time to see what you understand and what you may need to double check.
For the following questions, use your pencil and paper to record your answers down then click the text box to reveal the answers. Good luck!
1. What is the biggest planet in our Solar System?
Jupiter
2. How many Earth Units (EU) does it take to match the planets diameter in Question 1?
a. 2.0 EU
b. 11.0 EU
c. 5.0 EU
b. 11.0 EU
3. What planet is similar in size to Earth?
Venus
4. What other two planets are similar in size?
a. Mars & Saturn
b. Mercury & Neptune
c. Uranus & Naptune
c. Uranus & Neptune
5. What is the smallest planet in our Solar System?
Mercury
How did you do?
Remember, the more practice you get the better you become. You can find many sources online that will help you answer the many questions you may have to expand your knowledge.
For an example, I've included two videos below that are centred around cosmic scaling. These videos are produced and distributed by the Khan Academy online learning resource and two videos I enjoyed when I was learning about scales in our Universe.
The Khan Academy online resource is just an amazing tool I think everyone should get familiar with. You can find the website here ➡️ ➡️ Khan Academy
(Accessibility Note: Use the gear icon on the video player to turn on Closed Captions [CC] or to slow down the playback speed to 0.75x if you need more time with the data).
(Accessibility Note: Turn on Closed Captions [CC] or adjust the video playback speed to 0.75x in the player settings if the data moves too quickly).
These video lessons can be found here:
I challenge you to attempt the additional questions found on the
Cosmic Measurement Chart page. You'll need your calculator.
I challenge you to attempt the additional questions found on the
Cosmic Measurement Chart page. You'll need your calculator.
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