Caroline Herschel was a famous astronomer. She discovered eight comets, and made observations of nearby stars and distant galaxies. She did all this 200 years ago, during a time when women didn’t usually have jobs in science, and she was the first woman to be paid for her scientific work.

In this activity students should get an idea about what was known about the universe 250 years ago.  They should be able to compare it to their knowledge of the universe, and what lies inside and outside the solar system if you define the edge of the solar system as the Oort cloud.

Inside or outside

Inside the solar system:

  1. The sun.  This is about 0.01 AU across (1 AU is 1 astonomical unit - the distance between the Earth and the sun)
  2. Earth
  3. The Moon.  The Moon's orbit is 0.003 AU from the Earth
  4. Pluto
  5. The Kuiper Belt
  6. Halley's comet, which orbits the sun every 76 years.  Its furthest distance from the sun is 35.1 AU, the closest is 0.6 AU.

Outside the solar system:

  1. Proxima Centauri.  This is the nearest star to our solar system.  It is found 4.2 light years away (266,000 AU).
  2. The centre of our galaxy.   The sun is 27,000 light years (1.7 billion AU) away from the centre of our galaxy, the Milky Way.
  3. The Andromeda galaxy.  This galaxy not only outside the solar system, but it is outside our own galaxy.  It is 2.5 million light years (160 billion AU) away.

How big is the solar system?

You will need...

A playground or large outdoor area where you can use chalk on the ground
A tape measure
A long piece of string


A large indoor area
Masking tape
A tape measure
A long piece of string

How long will it take?

This could take one or two hours, depending on how long your class takes to calculate the distance to the different planets.  It will also take less time if you have different groups marking out and drawing the different planets' orbits at the same time.  You could ask the students to do the calculations in one class and then draw out the solar system in the next.

What to do...

Divide the class into groups.  You can have ten groups, giving responsibility of a planet to each one, leaving one group to work out the position of the sun and decide on a suitable scale.

Alternatively you can decide on the scale for the activity (or do this as a class), and divide the class into nine groups, one for each planet.  Each group should work out the positions of all the planets but should measure out and draw the orbit for only one of them.

Encourage the class to make the best use of the space they have.  If there is lots of space, a large scale will mean there is lots of room in the inner solar system, but Pluto and Neptune will be very far away.

When the class has finished they can have fun pretending to be the planets moving around in their orbits.  If your scale allows they may be able to model the orbits of the inner solar system, rotating as they orbit the sun.  Below is a list of orbital periods: how long in it takes in years for each planet to make one full orbit around the sun.

Mercury 0.2 years

Venus  0.6 years
Earth  1 years
Mars  1.9 years
Jupiter  11.9 years
Saturn  29.5 years
Uranus  84 years
Neptune 164.8 years
Pluto  247.7 years

The planets can be found anywhere on their orbit.  Have a look at a website like which will give you a map of where the planets are in their orbits of the sun right now.  They are very rarely lined up!


Curriculum Links

Expanding horizons

Working scientifically

Scientific attitudes

  • understand that scientific methods and theories develop as earlier explanations are modified to take account of new evidence and ideas, together with the importance of publishing and peer review

Analysis and evaluation

  • present observations and data using appropriate methods, including tables and graphs


Space physics

  • our Sun as a star, other stars in our galaxy, other galaxies
  • Ideas, political power, industry and empire: Britain, 1745-1901


Scottish Curriulum links


Planet Earth - Space

SCN 2-06a

By observing and researching features of our solar system, I can use simple models to communicate my understanding of size, scale, time and relative motion within it. [Note: level 2]

SCN 3-06a

By using my knowledge of our solar system and the basic needs of living things, I can produce a reasoned argument on the likelihood of life existing elsewhere in the universe.

SCN 4-06a

By researching developments used to observe or explore space, I can illustrate how our knowledge of the universe has evolved over time.


Number, money and measure - Powers and roots

MTH 4-06a

Within real-life contexts, I cause scientific notation to express large or small numbers in a more efficient way and can understand and work with numbers written in this form.

Number, money and measure - Measurement

MNU 3-11a

I can solve practical problems by applying my knowledge of measure, choosing the appropriate units and degree of accuracy for the task and using a formula to calculate area or volume when required.

MNU 4-1

I can apply my knowledge and understanding of measure to everyday problems and tasks and appreciate the practical importance of accuracy when making calculations.

Number, money and measure - Mathematics - its impact on the world, past, present and future

MTH 3-12a

I have worked with others to research a famous mathematician and the work they are known for, or investigated a mathematical topic, and have prepared and delivered a short presentation.

MTH 4-12a I have discussed the importance of mathematics the real world, investigated the mathematical skills required for different career paths and delivered, with others, a presentation on how mathematics can be applied in the workplace.


Expanding horizons

When Caroline Herschel was born, people knew a lot less about the universe than they do now.  They were familiar with five other planets, Mercury, Venus, Mars, Jupiter and Saturn, which were easy to see without a telescope.  Within her lifetime, two other planets, Uranus and Neptune, were discovered.  She was 30 when her brother William discovered Uranus using a telescope.  And just before she died, Newton's law of gravity was used to predict and find the position of the eighth planet, Neptune.

Artist's representation of planets


Why were sailors interested in astronomy?

Astronomy was used for navigation across the seas and oceans in the 18th century. Many astronomers were looking for ways to measure time accurately in the middle of the ocean, because this would help sailors calculate their exact position. Some astronomers calculated time by looking at how the moon moved in the sky, while others made observations of the moons of Jupiter. In the end, John Harrison invented a watch in 1764 that would keep accurate time at sea, allowing sailors to work out exactly where they were, without needing to observe the passage of objects in space.

While explorers like James Cook were using these new techniques to help them navigate around the globe, astronomers were exploring even further out into space.

Where does the solar system end?

The solar system is more than just its planets.  The edge is far, far away.  As the sun pours out its light and heat, tiny particles also speed out of the sun.  This is known as the solar wind, and it travels billions of miles out into space, until it collides with the dust and gas found between one star and the next.

Even further than that is a giant shell of comets called the Oort cloud. This is nearly a light year away from the sun (light from the sun takes one year to reach the Oort cloud), and about a quarter of the way to the nearest star.  Since some of its comets fall in towards the sun, the Oort cloud can be thought of as the edge of the solar system.

Key fact: The edge of the solar system is almost one light year away from the sun, where the Oort cloud - a collection of comets - lies.



Can you tell what can be found inside or outside the solar system?

Take the online quiz here,

or download the pdf worksheet.


How big is the solar system?

Download the pdf instructions here.

If you want to study the solar system, it is really helpful to actually visualise the scale of it, and the objects within it. You can do this by drawing out the planets' orbits around the sun in a scale model.

You will need...

A playground or large outdoor area where you can use chalk on the ground
A tape measure
A long piece of string


A large indoor area
Masking tape
A tape measure
A long piece of string

What to do...

First work out where the sun is going to be. To do this, measure the size of your area and work out where the middle is. Draw the sun in the middle with chalk, or mark the place with masking tape.

Now measure how far your planets can stretch, by measuring from the sun to the nearest obstacle or boundary in your playground or room.

Astronomers don't normally think in kilometres when they are looking at the solar system, because the solar system is far too big. Instead they compare distances between planets and other objects to the distance between the Earth and the sun: this standard distance is known as 1 astronomical unit, or 1 AU.

If the Earth is at 1 AU, then the other planets are at:
Mercury 0.5 AU
Venus  0.7 AU
Earth  1 AU
Mars  1.7 AU
Jupiter  5.5 AU
Saturn  10 AU
Uranus  20.1 AU
Neptune 30.4 AU
Pluto  49.3 AU

Marking out the sun and planets

You need to decide on a scale.  For example...

If Earth is 10 cm from the sun in your scale, Mercury is only 5 cm from the sun, and Pluto is nearly 500 cm (5 metres) away.  If you measured more than five metres to your boundary you can use this scale, if you measured a lot more, then use a bigger scale.

To work out the distance to each of your planets you need to make a calculation.

1 AU = 10 cm (or whatever scale you choose to use)
Starting with Mercury...
0.5 AU = 0.5 x 10 cm = 5 cm

Download and print the table from here, and use it to fill in your calculations.

Although you can draw the orbits of the planets, you cannot draw the size of the planets to scale like this: they are much, much smaller than their distance from the sun.  With a scale of 1AU = 10cm, the sun would be just 1mm across!

Now you need to draw on your planets. Start with Pluto. Measure the distance to Pluto on the piece of string. You may need to tie two pieces together if it is particularly far away. Ask someone to hold one end of the piece of string at the sun in the centre of your playground. Pull the string tight and mark the position of the planet at the far end of the string. Walk round, keeping the string tight and mark the ground at the end of the string. You should complete a full circle - be careful not to trip anyone up on the way round!

Marking out the sun and planets (2)

Next, measure out the distance to Neptune and repeat. Keep going until you have drawn circles for all the planets.

Now draw a planet somewhere on each of the orbits.  Or, if you have room, pretend to be a planet and see how long it takes you to orbit the sun.  Don't forget planets also rotate as they go round the sun!

Beyond the planets

The solar system is not just made up of planets.

The Kuiper Belt is an enormous disk of asteroids between 30 and 50 AU from the sun. This is outside the orbit of Neptune. Pluto is thought to be the largest Kuiper Belt object.

Even further out is the Oort Cloud. This is a spherical shell of rocks and comets. It is found a staggering 50,000 AU from the sun.  Can you work out how far away this is from your sun, using your scale? Have a look on a map to see if this lies inside or outside your town!