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Journey · Space

How small are we in the universe?

From the planets to the light year: getting a feel for scale

Steps
5
Total time
1 h 23 min
Simulations
7
Try the first step See the steps
The Milky Way in a star-filled night sky
If the Sun were a ball one metre across, the Earth would be a bead nine millimetres wide.

Photo: Greg Rakozy / Unsplash

Why is this question interesting?

In textbook pictures of the Solar System, the planets are lined up side by side. If they were drawn to true scale, they wouldn't fit on the page: the Solar System is mostly empty space. Sizes in space are hard to grasp, because none of the measures we use in everyday life ever gets that big.

On this journey you'll first put the planets in order and compare their sizes. Then you'll widen the scale and map the distances onto your own neighbourhood and city, and you'll see why the distance light travels in a year is used as a unit of length. Realising that when you look at a star you are really looking into the past is one of the best ways to get a feel for scale.

Then you come back home: how does the Earth spinning on its axis create night and day, and how does the Moon's orbit create its phases? The journey ends with understanding the daily rhythm of a small planet in a huge universe.

Steps

We suggest going in order; each step builds on the one before. You can try every lesson’s simulation without an account.

  1. Step 118 min

    The Solar System and the planets

    First, get to know our neighbours: the order of the eight planets and their real sizes.

    • Planet observatory
    • Mini quiz

  2. Step 217 min

    The scale of space

    Scale the distances down until they fit; that's when you see how big the empty space really is.

    • Number line
    • Sorting
    • Mini quiz

  3. Step 315 min

    The light year: measuring distance with time

    When kilometres aren't enough, we use the distance light travels as our measure. Looking at a star is looking into the past.

    • Number line
    • Planet observatory
    • Mini quiz

  4. Step 415 min

    The Earth's rotation and day and night

    Come back home from the big scale: the Sun isn't rising and setting; we're the ones turning.

    • Number line
    • Mini quiz

  5. Step 518 min

    The phases of the Moon

    The Moon's shape doesn't change; the lit part we can see does. Put the phases in order and see why.

    • Sorting
    • Mini quiz

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