1 The sun is a giant ball of gas consisting primarily of hydrogen and helium. Nuclear fusion reactions continually take place on the Sun. In this reaction four nuclei of hydrogen atoms fuse together to form a helium atom and in the process radiant energy is produced and this is sent out into space. Some of this solar energy travels through space to Earth as electromagnetic radiation travelling at the speed of light. The electromagnetic radiation travels as gamma rays, X-rays, ultraviolet and visible light, infrared radiation, microwaves and radiowaves.
2 a b
Mercury
Neptune c d
Earth
Mars
3 a b
F
T
F
F
The diameter of Pluto is smaller than the diameter of all the other planets.
Students may put their own argument here. Some students will argue that as Pluto has always been a planet it should continue to do so. This would save the expense of having to print new textbooks and posters etc. Others will argue that because Pluto is so small and because it crosses the orbit of Neptune it does not meet the criteria for a planet.
T 4 a d e b c f g
F
T h T
5 Saturn and Uranus don’t have a firm surface as they are giant balls of gas. The craters on Mars and
Mercury are the result of collisions between the planets and objects travelling through space such as comets and asteroids.
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6 Jupiter is the largest planet and it has the most moons so this suggests that their conclusion is true.
However, Uranus and Neptune are of similar sizes but they have very different numbers of moons so this would tend to contradict the conclusion. The table below makes the information easier to analyse and shows that there is no clear relationship between size of the planet and the number of moons.
Planet No of moons
Mercury No known satellites
Mars 2 moons
Earth 1
Neptune 13 moons, five have yet to be named
Uranus 21 named moons and 6 unnamed moons
Saturn 34 named satellites
Jupiter 63 satellites including 4 large moons
Diameter (km)
4800
6794
12 756
49 532
51 118
120, 536
142 984
7 Students will discuss their own experiences with Practivity 7.1.
8 Moons are natural satellites that rotate around a planet.
9 Asteroids are rocky and metallic objects that orbit the Sun but are too small to be considered planets.
Asteroids range in size from Ceres, which has a diameter of about 1000 km, down to the size of pebbles.
Comets are are left over from the formation of stars and planets billions of years ago. Comets that we see in our solar system start out as big chunks of rock and ice just floating around in something called the Oort Cloud. When the gravity from a large passing body, like a star, becomes strong enough, some large chunks of ice get pulled away from the cloud and head toward the Sun. As that ball of ice gets close enough to the Sun, the Sun’s heat begins to melt some of the ice that makes up the comet.
The melted ice becomes a gaseous tail that extends away from the source of the heat.
10 In the paragraph students need to discuss the following.
•
•
The increasing population on Earth.
The time and energy that would be required to establish a colony on a nearby object such as the moon against the time and energy required to transport people and materials to a distant object such as Europa.
• The need to provide for the basic needs of the people i.e. food to eat, air to breathe and water to drink.
• The different gravitational pull on different space objects and the effect of this on the human body.
1 a Day time b Night time
2 c d a
Night time
Night time
Difficulties experienced with Practivity 7.2 could include seeing which part of the model was in darkness and in the light and understanding the time it takes for the globe to make one
Oxford Big Ideas Science 1 ISBN 978 0 19 556715 1 © Oxford University Press Australia

6
7
3 complete spin on its axis. Getting the tilt of the globe correct so that students can understand the different temperatures experienced in the different seasons is also challenging for some students. b Students will provide useful feedback here that can inform the teacher of the need to do further work on this topic.
The images show what the Earth looks like as it spins and the lights on in the night time in cities around the world can clearly be seen.
4 All planets would experience day and night because they are spinning on their axis so for part of each day part of the planet will be in darkness.
5 Venus would have the longest day as it takes 243 days to make a complete turn on its axis. b c
The Sun rises first in Sydney. a The Earth viewed from space is a sphere .
The Earth spins on its
The Earth takes axis . This is called twenty-four rotation .
hours to rotate on its axis.
8 d e
Australia is on the bottom half of the Earth. This is called the
A hemisphere is half of a sphere. southern hemisphere f
23.5°
As the Earth rotates, only half of it faces the Sun at any one time.
.
9 The angle of the tilt is always the same.
10 When the northern hemisphere is slanted towards the sun it is summer for them. At the same time it is winter for us here in Australia
11 It takes the earth 365.25 or 365 1/4 days to revolve once around the sun which is our year. We can't use 1/4 of a day, so these 1/4 days are saved up until we get 4 of them. Four 1/4s makes one more full day. This full extra day is given to February.
12 Students’ own drawings.
13 a b
T
F – The length of day on each planet is determined by the time it takes for the planet to spin on its axis. c d e f g
There is a leap year every four years because the amount of time the Earth takes to travel around the Sun is actually 365 1 /
4 days. In the leap year the 4 x ¼ days are added together to make a full day.
T
T
Partly TRUE – When the Moon and the Sun are aligned the tides are higher due to the pull of gravity from the Sun.
T
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h i j k l
F – The moon does not produce any light.
F – Craters are found on all the rocky planets but planets which don’t have an atmosphere tend to have more craters.
T
F The Sun provides solar energy due to the nuclear fusion reactions taking place within it.
T m F Mercury takes only 88 days to orbit the Sun so it orbits much faster than the Earth.
1 You can see the clouds, the oceans and the land masses.
2 The clouds are in the troposphere.
3 The clouds are an important part of the water cycle. They carry rain and snow to the hilly and mountainous areas where it is dropped. The rain becomes part of water in the ground and flowing in rivers and creeks. It is essential for plant and animal life.
4 The clouds block out the sunlight. On cloudy days you will notice that temperatures are cooler as less solar energy gets through to be reflected from the Earth or absorbed by the Earth.
5
6
If the Earth was covered with lots of pollution and dust filled clouds it would be much cooler on Earth.
Students’ own answers based on the data available on the day.
7 If the amount of sunlight getting through the clouds is reduced there will be less energy available for plants to use in photosynthesis. In areas where it is very dark due to the effect of the clouds the plants may die as they need the regular supply of sugar provided through photosynthesis.
8
9
Other activities which could have an impact on the Earth’s climate are the eruption of volcanoes, changes in the Sun’s brightness, deforestation, changes in the concentration and type of gases in the atmosphere – e.g. increased levels of carbon dioxide and methane or increased amounts of dust or smog.
Students’ own answers.
101 Some suggested answers are listed below. Students will have some other ideas also.
FOR Space travel
Enables us to learn about other planets and space itself
We might find a planet where we could set up another colony or find resources that could be useful on Earth
There are lots of spin-offs from the space program that have been used to improve life here on Earth
A new manned spaceflight program would do a lot to restore public enthusiasm for space and for science generally.
AGAINST Space travel
Uses money that could be put to good use on Earth
The funding used here on Earth could solve some of the major problems such as world hunger, climate change and pollution
The space travel adds to the pollution of space itself
We are unlikely to ever be able to colonise another planet as they are too far away so we should focus instead on keeping the Earth’s environment in as good a condition as we can. It’s all we have!
Oxford Big Ideas Science 1 ISBN 978 0 19 556715 1 © Oxford University Press Australia

By learning more about other planets we also learn lots more about planet Earth.
It is elitist. The poor people of the world will never benefit from space travel.
Investment in the space program provides employment and economic growth for the countries involved.
It is dangerous. All of the astronauts on the
Challenger Space Shuttle were killed. The risk is too great.
Oxford Big Ideas Science 1 ISBN 978 0 19 556715 1 © Oxford University Press Australia