The size and nature of our Solar System is truly awe inspiring, and things are going to get even more exciting once the New Horizons spacecraft reaches Pluto in 2015. But just how much do you know about the Solar System?

In this lesson you will investigate the following:

• How did the Solar System form?

• How big is the Solar System?

• How do we measure distances in the Solar System?

• Which has a longer “day”, Mercury or Jupiter?

How do you organise a party in outer space? You planet!

This is a print version of an interactive online lesson. To sign up for the real thing or for curriculum details about the lesson go to www.cosmosforschools.com

Earth and Space Sciences

The Solar System: Cosmic encounter with Pluto

Introduction: The Solar System

In some ways 1977 was the beginning of the modern world, with the first computers on sale to the public – and the first homevideo games. It was also the year that the first Star Wars movie came out. But Earthlings didn't limit space travel to fiction – they alsolaunched two identical spacecraft to Jupiter and Saturn: Voyagers 1 and 2.

The Voyagers successfully completed their mission making discoveries such as the active volcanoes on Jupiter's moon, Io, andlearning details about Saturn's rings. They had only been made to last five years but were still both going strong, so NASA extendedtheir mission. Voyager 2 went on to take a look at the two outermost planets, providing us with the first close-up pictures of Uranusin 1986 and then arriving at Neptune three years later. Even though they move at speeds in the order of 20 kilometres a second itstill takes a while to get anywhere in the Solar System!

It's amazing that 38 years after they were launched the Voyagers are still gathering data and transmitting it back to Earth. As of 2014they are at the edge of the Solar System and Voyager 1 is now the most distant man-made object in space. Both Voyagers are in azone where the Sun's radiation drops off, teaching us about the transition into deep space.

We haven't finished with the Solar System though. In 2006 the New Horizons spacecraft was launched to fly to Pluto. Just becauseit's no longer a planet doesn't mean Pluto and its five moons won't deliver some exciting new discoveries. Data starts arriving backon Earth in January 2015.

Both of the Voyagers carry gold-plated discs with sounds and images portraying the diversity of life and culture on Earth. Why? Justin case, one day, the spacecraft are found by intelligent aliens. If they can follow the instructions written on the discs they will hearthe sounds of surf and thunder, of birds, whales and other animals, and of greetings in fifty-five human languages. They will hearmusic from different human cultures and see pictures of life on Earth.

The Solar System is a huge and complex place with many discoveries to be made. And it is our home.

Read the original Cosmos blog post here.

Left: An illustration of one of the Voyager spacecrafts as it might look right now at the edge of our Solar System. Right:The curious cover of the gold-plated disc carried by the spacecraft. The markings are instructions on how to use the disc.

Do you think that an alien would understand them?

Question 1

Describe: When New Horizons has finished sending back all its data from Pluto there will be free space on its hard drive. There iscurrently a crowd-sourced project to load the drive with messages from Earth, just like the Voyager discs. What sounds and imageswould you choose to go onto the 2015 version of the Voyager gold discs? Why?

Gather: The Solar System

Space exploration has provided us with spectacular photographs of the bodies in our Solar System. Left to right: the Sun,Jupiter and Neptune.

The Voyager and New Horizons spacecrafts were sent on extraordinary missions to explore our Solar System. But what is the SolarSystem and how did it come to be?

The Solar System

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Question 1

Recall: The nebula that eventually formed our Solar Systemwas created by the birth of a star.

True

False

Question 2

Recall: The Earth started to form at the centre of a vast spiral ofdust.

True

False

Question 3

Recall: Type the missing words into the right hand column of the table below.

Our Solar System is approximately ________ light-years from the centre of ourgalaxy.

________ are clouds of dust and gas that result when a star explodes.

________ pulls the dust and gas together to form planets and stars.

The outer gas planets of the Solar System are ________, ________, ________ and________.

The inner rocky planets of the Solar System are ________, ________, ________ and________.

The estimated lifespan of the Sun is ________ billion years

Although the ignition of the Sun cleared much of the debris in the Solar System, some things other than planets still remained.

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Question 4

Recall: The asteroid belt is located between the orbits of

Jupiter and Saturn

The Sun and Earth

Earth and Mars

Mars and Jupiter

Question 5

Identify: Which of the following are considered to be part of ourSolar System?

Planets

Asteroid belt

Milky Way

The Moon

Sun

Nebulae

All of the above

Did you know?

Did you know that Pluto, that orbits the Sun beyond Neptune, used to be classified as a planet? But in 2006 the InternationalAstronomical Union changed the definition of a planet and Pluto didn't fit this new definition, so was reclassified as a "dwarf planet".

So far we have explored some of the major bodies that make up our Solar System and how it was formed. But there is anotherimportant piece to this puzzle: everything in the Solar System is moving.

The planets, their moons and the Sun are all moving around each other in elliptical movements called orbits. The Sun, planets andmoons are also all constantly spinning, like a basketball spinning on your finger. But why do they spin?

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what makes up the Solar System

the motion of bodies in the Solar System.

Question 6

Construct: Summarise everything that you know and have learned about the Solar System into a graphic organiser. Create yourorganiser on paper and upload a photo of it.

Your organiser should include:

the formation of the Solar System

Process: The Solar System

The Sun and eight planets of the Solar System shown in scale according to their size, but not according to the distancebetween them. Can you name all the planets?

The distances between objects in space are immense. For instance, the distance between the Sun and Jupiter is 778,547,200 km,and the nearest star (Proxima Centauri) is approximately 39,900,000,000,000 km away.

The numbers are so big it's difficult for people to grasp them and it's easy to make mistakes with that many zeros! So astronomershave developed two other units for measuring astronomical distances – one for the Solar System and another for galaxies, starsand other objects outside the Solar System.

Astronomical unit

In the Solar System astronomers use the "astronomical unit" (AU). One AU is the distance from the Earth to the Sun (149,600,000km). On this scale Jupiter is about 5 AU from the Sun.

Light-year

A "light-year" is the distance that light travels in one year. One light-year equals 9,460,500,000,000 km. It's a very long way! Thatmakes Proxima Centauri 4 light-years away.

Astronomical distances

Question 1

Calculate: In July 2015, when the New Horizons space probe flies past Pluto, the Earth will be 4,920,000,000 km away. Calculate thisdistance in AU.

Orbits

Model of the planets orbiting the Sun. It simply shows which planets are faster or slower than others.

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Question 2

Think: The time it takes a planet to complete one orbit is called its orbital period.

Part A: Fill in the empty cells in column 2 with the number of orbits the planets make in the 25-second video.

Part B: Listed below are the actual orbital periods of the eight planets, measured in Earth years and months, but they are out oforder. Put the values into the third column, matching them to the correct planets.

1 year 11 months | 84 years | 3 months | 165 years | 29 years | 7 months | 12 years

Planet (in order from the Sun) Number of orbits in video (Part A) Orbital period (Part B)

Mercury 7

Venus 5.5

Earth 1 yr

Mars 3.5

Jupiter

Saturn 2

Uranus

Neptune 1

Question 3

Planet race: If Mercury, Venus, Earth and Mars are travelling anti-clockwise in the diagram below, show where they will be in sixmonths. If any of them have completed any orbits, write the number of completed orbits beside the planet's starting position.

For example: the Earth's orbital period is 12 months. So in six months' time it will be half way around its orbit (6 ÷ 12 = 0.5).

Tilt and rotation

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Question 4

Think: The above video shows the angle of tilt and rotational periods of the planets and Pluto.

Part A: Count the number of rotations in the 25 seconds of the video to fill in the empty cells in column 2.

Part B: The rotational period data for Mercury, Jupiter and Neptune has been mixed up. Can you complete the table with the valueslisted below?

16 Earth hours | 10 Earth hours | 2 Earth months

Planet Number of rotations in video (Part A) Rotation period (Part B)

Mercury Barely moves

Venus Barely moves 8 months

Earth 1 day

Mars 11 1 day and 1 hour

Jupiter

Saturn 28 10.5 hours

Uranus 17 hours

Neptune 17

Question 5

Consider: One Earth rotation is equivalent to:

One month

One day

One year

One day and night

One season

Question 6

Reason: Describe one or more of the effects if the Earth's speed of rotation was double what it is.

Question 7

Hypothesise: Describe some of the effects you might see if the Earth's axis of rotation changed to be the same as Uranus's. If thishad always been the case, do you think life would have evolved in the same way it did?

Apply: The Solar System

Experiment: Modelling the Solar System

Most of the representations of the Solar System that you see in textbooks are not to scale. In this exercise you will find out why.

To create a model of the Sun and the eight planets of the Solar System showing their relative sizes.

1 fit ball, approximately 700 mm diameter

modelling clay

ruler

Calculate the sizes of the planets using the same scale that represents the Sun as the fit ball. Make planets from the modellingclay using the ruler to check the diameters.

Part 1: Size model

Background

Aim

Materials

Procedure

Results

Question 1

The Sun is 1,390,000 km diameter. The fit ball is 700 mm diameter. A simple calculation shows us that in our model 1 mm isequivalent to approximately 1,986 km ( ).

To make things a bit easier we will round up and use the following scale:

1 mm represents 2,000 km

The diameters of all the planets are given in the table below. Using this scale calculate the sizes of all the planets for the model,and fill in the table. Round to the nearest millimetre.

The calculation for Mercury is worked out for you below:

The diameter of Mercury is 4,880 km. Divide this by 2,000 to give an answer in millimetres.

Rounding and using a fit ball to represent the Sun, Mercury would be 2 mm in diameter!

= 19861,390,000700

= 2.444, 8802, 000

Planet Diameter (km) Scaled diameter (mm)

Sun 1,390,000 700

Mercury 4,880 2

Venus 12,100

Earth 12,800

Mars 6,790

Jupiter 143,000

Saturn 121,000

Uranus 51,100

Neptune 49,500

Question 2

Use pen and paper to label your planets and upload a photo of them below.

To create a model of the Sun and the eight planets of the Solar System showing the relative distances between them.

modelling clay

9 flags on sticks

open space, e.g. a playing field, 100 m long.

Part 2: Distance model

Aim

Materials

1. Calculate the scale you need to use so that the model will fit in a straight line 100 m long.

2. Calculate the diameter of the Sun at that scale and make a ball of the right size to represent the Sun out of the modelling clay.

3. Calculate the distances between the Sun and planets using the same scale and fill in the table below with the values.

4. On the playing field, place the Sun at one end of the 100 m strip and push in a flag beside it.

5. Pace out the distances to each planet and mark the positions with flags.

Note: One very long pace is about one metre.

Procedure

Question 3

The distance from the Sun to Neptune is 4,500,000,000 km. We need to scale this down to 100 m.

What is the scale we need to use?

Question 4

The Sun is 1,390,000 km diameter. What diameter should your model Sun be using the scale you just calculated?

Question 5

Complete the table below with the distances to each of the planets in the model, using the scale you calculated.

To help make sure you're on track we've put in the distance to Mercury.

Planet Distance from Sun (km) Scaled distance (m)

Mercury 57,000,000 1.3

Venus 108,000,000

Earth 150,000,000

Mars 228,000,000

Jupiter 779,000,000

Saturn 1,430,000,000

Uranus 2,880,000,000

Neptune 4,500,000,000

You are now ready to go and make your Solar System distance model!

Results

Question 6

Upload a photograph of your model. Make sure to stand perpendicular to the line of the planets so that you get a good idea of thedistances.

Tip: For the photo, you and your classmates may wish to stand next to the Sun and planets holding signs to indicate what you're standingnext to.

Discussion

Question 7

In the distance model you placed the planets' positions in roughly a straight line. Is this a true representation of the Solar System?Why or why not.

Question 8

How big would the planets be if you sized them at the correct scale for the distance model?

Question 9

How far away from the fit ball would your model of Neptune be if you used the scale 1 mm = 2,000 km for the distance model?

Career: The Solar System

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Question 1

Research: You decide to make it your life's mission to find another Earth-like planet in the Universe -- one that could harbour alienlife. What would be the ideal job to help you succeed in your mission? What would you need to study in order to get the job?

Cosmos Lessons team

Lesson authors: James Driscoll and Deborah TaylorEducation editor: Jim RountreeEducation director: Daniel Pikler

Image credits: iStock, Kate Patterson MediPics and proseand Mirela TufmanVideo credits: The Cosmos is Also Within Us, SciShow, SolarSystem Videos, Steven Sanders, New York Times