Mini Scientists: Chalk Planets

Recently, T and I have been learning about space. We’ve done this topic a few times now, first when she was about two and a half, again last year and then again this summer. It’s something which we can delve deeper into every time we study it, which is really fun! This time, it happens to have fallen very close to the 50th anniversary of the first moon landing. I could tell you it’s excellent planning on my behalf, but in truth it is a happy coincidence!

One of the things I wanted to explore with her was the relative size of the planets – the difference is so enormous, that most illustrations don’t draw them to scale! Since we’re lucky enough to have a large garden wall, I decided we would have a go at drawing some chalk planets to scale.

It’s a great activity for both Science and Maths as it involved measurement; learning how to draw circles accurately; and introducing vocabulary such as radius and circumference; as well as learning about the relative size of the planets; recapping their order in the solar system; and recalling other facts we had learned about them.

Image of a brick garden wall with sky and trees above and grass below. On the walk is a chalk drawing of the planets.

For this activity, you will need:

  • Some large sticks of chalk
  • A length of string around one metre long
  • A ruler or measuring tape
  • A space to draw. It needs to be a minimum of 70 cm high and around 3 metres wide

I began by looking up the sizes of each planet online, and found their radii in kilometres. To convert these measurements to a size we could draw, I divided the measurements by one thousand, and then changed the unit of measure to centimetres. The resulting radii for each planet are approximately:

  • Mercury: 2.4 cm
  • Venus: 6 cm
  • Earth: 6.4 cm
  • Mars: 3.4 cm
  • Jupiter: 69.9 cm
  • Saturn: 58.2 cm
  • Uranus: 25.4 cm
  • Neptune: 24.6 cm

We tied the chalk to the end of our string and then used a ruler to measure the appropriate radius from the chalk along the string and marked the point. I rounded the measurements to the nearest half centimetre to make it easier for T to find them. 

We used the string as a rudimentary compass. I held the marked point still in the centre, while T carefully drew around the circumference. And there you have it – a scale drawing of the planets at one hundred millionth of the size!

The comparative size of the sun was so big that we didn’t have the space to draw it, but we measured out how wide it would be and also worked out that it would be taller than our house! Quite mind-blowing, given that Earth was smaller than my hand-span!

What she is learning:

  • Order of the planets
  • Relative size of the planets
  • Measuring using a ruler
  • Drawing circles accurately
  • Related mathematical vocabulary
Title image for pinterest

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