XXX Background information The solar system Our solar system is made up of the Sun, the planets, the dwarf planets, moons, asteroids and comets. The Sun is the star around which everything orbits. There are eight planets: four inner rocky planets (Mercury, Venus, Earth, Mars) and four outer gas giants (Jupiter, Saturn, Uranus, Neptune). Our Earth is the only planet known to support life. All of the planets, except Mercury and Venus, have moons. Saturn, with its thirty moons, has the most. How we know about the planets From the beginning of the seventeenth century, when telescopes were invented, humans have been studying the stars and the planets. In the past fifty years, robot probes have travelled across our solar system and have sent back images and data. Dwarf planets The term dwarf planet was created in 2006 by the International Astronomical Union (IAU) to describe a new type of astronomical object. The IAU defines a dwarf planet as a celestial body that: is in orbit around the Sun is big enough for gravity to squash it into a round ball. The thing that distinguishes a dwarf planet from other planets is that it has not cleared other things out of the way in its orbital path around the Sun, so there are similar objects to itself at roughly the same distance from the Sun. Pluto was downgraded from a planet to a dwarf planet in 2006. When it was discovered in 1930, Pluto was named the ninth planet in our solar system. In recent years, astronomers have found that Pluto is part of what is known as the Kuiper Belt, which contains a number of other objects similar to Pluto. In 2005, astronomers discovered Eris, a celestial object even bigger than Pluto. A year later, a large number of astronomers decided Pluto, Eris and Ceres (an object found in the asteroid belt), should become the first three dwarf planets. Astronomers believe that as many as seventy more objects in our solar system could be named as dwarf planets in the future. Asteroids Asteroids are rocks or small planets. Hundreds of rocks form a ring between the orbits of Mars and Jupiter and this is known as the asteroid belt. Ceres is a dwarf planet in the asteroid belt. Comets A comet is an object made of rock, dust and ice that orbits the Sun. Its orbit goes near to the Sun and out beyond Pluto. As it goes near to the Sun, some of the ice melts and forms a tail of gas and dust. The Milky Way Galaxy Our solar system belongs to the Milky Way Galaxy. A galaxy is a huge cluster of stars. Scientists believe that our galaxy could contain as many as 400 billion stars. Everything in the Milky Way is slowly turning around its bright centre. The universe The universe is everything that exists in space. It is thought that the universe could contain as many as 100 billion galaxies. Measuring distances in space The distances between stars are so huge that they are measured in light years rather than kilometres. A light year is the distance light travels in a year. Light travels at just under 300 000 kilometres per second, so one light year is 9.5 trillion kilometres. Our nearest star is 4.22 light years away and the Milky Way is 100 000 light years from one end to the other. The Sun and ancient civilisations Many ancient people worshipped the Sun as a god and created legends and myths about it. The ancient Greeks called it Helios, the ancient Egyptians called it Amon-Re or Ra and the ancient Romans called it Apollo. The Aztecs used the name Huitzilopochtli. Aztec priests took the throbbing hearts from living people and offered them up in sacrifice to Huitzilopochtli. 5
XXX The Moon and ancient civilisations For many ancient people, the Moon was considered to be an object of great beauty and mystery. Both the ancient Greeks and Romans worshipped the Moon as a goddess. The Romans called her Diana and the Greeks called her Artemis. The flat Earth Until the fourth century BC, people believed that the Earth was flat. Aristotle, the Greek philosopher, introduced the idea that the Earth was a sphere, based on the following observations and evidence: When a ship sails away, it does not just get smaller and smaller as it would if the Earth was flat. Instead the hull of the ship disappears first, followed by the upper part of the ship and then the very top. When people travelled far to the North they noticed that some groups of stars disappeared over the horizon, while new groups appeared over the opposite horizon. If the Earth was flat, then wherever you stand on the Earth, you would see the same groups of stars in the sky. During a lunar eclipse, the Earth comes between the Sun and Moon. When this happens, the Earth s shadow can be seen on the surface of the Moon. The shadow of the Earth is curved and not straight. Early science and the solar system For centuries, people believed that the Earth was at the centre of the universe, and anyone who suggested otherwise risked being sent to prison or being killed. In 1543, Polish astronomer Nicolaus Copernicus suggested that the Earth and the other planets all went around the Sun. In Italy, at the beginning of the seventeenth century, Galileo Galilei used the newly invented telescope to show other astronomers that Copernicus had been correct and that the Sun was in fact at the centre of our solar system. Day and night The Earth spins on its axis as it orbits the Sun. It takes 24 hours for the Earth to rotate once. The part facing towards the Sun is in daylight while the part facing away from the Sun is in darkness. The Earth is tilted at 23.5 degrees on its axis and is always tilted in the same direction as it travels around the Sun. This means that when the Northern hemisphere is tilted towards the Sun, places in this hemisphere get more than 12 hours of daylight, while places in the Southern hemisphere are tilted away from the Sun and get less than 12 hours daylight. Time zones The Earth spins in an anti-clockwise direction, which means that countries to the east of the UK come into sunlight before we do. These countries set their clocks so that they are ahead of ours. Countries to the west of the UK set their clocks behind ours. If we travel east we have to move our clocks forward, while if we travel west we have to move our clocks back. Apparent movement of the Sun across the sky The Sun rises towards the east and sets towards the west. During the day it appears to follow a curved path across the sky. This apparent movement is not caused by the movement of the Sun, but by the Earth spinning on its axis. By using a shadow stick and observing the shadows formed throughout a day, it is possible to track the path of the sun across the sky. If the shadow made by the stick is pointing to the east, then the Sun is in the west. If the shadow is short the Sun is high, and if the shadow is long, the Sun is low in the sky. Health and safety: Children should be reminded about the dangers of looking at the Sun. The Sun s changing path throughout the year Both the height and length of the Sun s path across the sky change during the year. The Earth is tilted at 23.5 degrees on its axis. When a hemisphere is tilted towards the Sun, the Sun appears to rise high in the sky during the day and the amount of time that it spends in the sky is longer and so are the days. When a hemisphere is tilted away from the Sun, the Sun does not appear to rise as high in the sky. The time that it spends in the sky is shorter and so are the days. When either of the poles is tilted away from the Sun, places near the pole receive no sunlight and are in darkness 24 hours each day. When either of the poles is tilted towards the Sun, places near the pole are in sunlight 24 hours each day, so that even in the middle of night, it is still daylight. 6
The seasons The Earth takes one year to orbit the Sun. When the Earth is on the part of its orbit where the northern hemisphere is tilted more toward the Sun, it is summer in the northern hemisphere and winter in the southern hemisphere. When the northern hemisphere is tilted away from the Sun, it is winter in this hemisphere and summer in the southern hemisphere. So while the northern hemisphere is having summer, autumn, winter, and spring, the southern hemisphere is having the opposite: winter, spring, summer and autumn. Leap year The Earth actually takes 365.25 days (or full rotations) to orbit the Sun. This means that every four years there is an extra day and rather than 365 days, that year has 366 days. It is known as a leap year. The Moon in orbit The Moon orbits the Earth in an anti-clockwise direction, once every 27.3 days. It also takes 27.3 days to spin around once on its axis, which means that the same side of the Moon always faces Earth. The side of the Moon that we never see is called the far or dark side of the Moon. Phases of the Moon The Moon does not produce light of its own but reflects the light from the Sun. The Sun only lights up the half of the Moon that faces towards it. As the Moon moves around Earth, we see different parts of the half that is lit by the Sun. The different shapes that we see are called phases and have the following names: New Moon: when the Moon is lined up between the Earth and the Sun and the lit side of the Moon is facing the Sun and not Earth. The Moon cannot be seen from Earth. Waxing crescent: when a small crescent section of the Moon can be seen. The Moon is said to be waxing when the crescent is getting larger and the Moon is moving towards a full Moon. Waxing half Moon: when half of the lit-up Moon can be seen and the Moon is moving towards a full Moon. Gibbous Moon: the Moon continues to wax and now more than half of it is lit up. Gibbous means having a hump. Full Moon: about two weeks after the new Moon, the Earth is now lined up between the Sun and the Moon and the Moon s face can be seen as a bright full circle in the sky. Waning gibbous: the full Moon shrinks down to a gibbous Moon. A waning Moon grows thinner each night. Waning half Moon: again we see one half of the full face of the Moon. Waning crescent: when a small section of the Moon can be seen and the Moon is moving towards a new Moon. New Moon: back to the new Moon again and the full cycle of phases is complete. This full cycle takes about 29.5 days. Space exploration the future Probes continue to travel into our solar system, sending back data and images. In the future, scientists hope that these robots will land on planets, comets and asteroids and bring back samples to Earth. Astronauts from all over the world regularly travel into space on board a space shuttle. Some now live and work in space, spending months at a time doing experiments on board the International Space Station. NASA, the USA s space agency, has said that it would like to send astronauts back to the Moon by 2020. They would leave equipment and supplies behind, and in the future these might be used by other astronauts to build a permanent base on the Moon. In years to come, NASA would also like to send the first human to Mars. 7
Find out more Use the following websites to keep up to date with developments in space science. Please be aware that a number of websites still categorise Pluto as a planet rather than a dwarf planet. Earth, Sun and Moon www.earthsunmoon.co.uk/ Play the game on this highly interactive site and find out about the Earth, Moon and Sun at the same time. Earth, Sun and Moon www.bbc.co.uk/schools/ks2bitesize/science/physical_ processes.shtml Interactive activities, revision and a quiz from BBC s KS2 Bitesize. Ask an astronomer: Why is Pluto not a planet any more? www.youtube.com/watch?v=9b25dpq9ory This video, presented by Dr. Robert Hurt from the Spitzer Science Centre, uses simple animations to explain why Pluto has been downgraded from a planet to a dwarf planet. Solar system www.bbc.co.uk/science/space/solarsystem/ A guide to the solar system from the BBC. Solar system exploration: planets solarsystem.nasa.gov/planets/profile.cfm?object=sol arsys&display=kids Facts and information about the planets in our solar system from NASA. Solar system exploration: missions sse.jpl.nasa.gov/missions/index.cfm Facts and information about the robot probes that explore our solar system. Mars online photo gallery quest.arc.nasa.gov/mars/photos/index.html Images of Mars from NASA. NASA Kids Club: The Expedition Crew www.nasa.gov/audience/forkids/kidsclub/flash/ nowinspace/crew_18_on_iss.html Learn more about life in the International Space Station with NASA s Kids Club. Planet comparison www.sciencenetlinks.com/interactives/messenger/ psc/planetsize.html This site allows you to choose any pair of planets and to compare them. Build a solar system www.exploratorium.edu/ronh/solar_system/ Use this online spreadsheet when building a scale model of the solar system. NASA Eclipse website eclipse.gsfc.nasa.gov/eclipse.html Use this website to find out when the next lunar and solar eclipses are scheduled to happen. Earth and Moon viewer www.fourmilab.ch/earthview/vplanet.html View a map of the Earth showing the day and night regions in real time, and a map of the Moon from Earth. Alien safari solarsystem.nasa.gov/kids/index.cfm Go on NASA s Alien Safari and discover the most extreme organisms on Earth and what they tell us about the search for life on other planets. World time zone map www.worldtimezone.com/datetime.htm A world map showing current time across the world. Sunrise, sunset and day length www.childrensuniversity.manchester.ac.uk/ interactives/science/earthandbeyond/sunrisesunset. asp Use this Children s University of Manchester website to learn how sunrise, sunset and day length change through the year. UK sunrise and sunset times map www.canterburyweather.co.uk/sun/ukmap.php See how sunrise and sunset times within Britain can vary on a particular day, with this Canterbury Weather website. 8
Planet profile AS1 Name of planet: Illustration: Time to orbit the Sun: Time to turn on its axis: Distance from the Sun: Distance from Earth: Size: Number of moons: Rings? (yes/no) Surface and atmosphere: Temperature: Other information: BBC Active iposter Earth, Moon and Sun
Earth, Moon and Sun: similarities and differences AS2 Which words and phrases apply to the Earth, Moon and Sun? The first has been done for you. Sun Earth Moon planet star moon sphere part of the solar system orbits the Earth orbits the Sun made of rock and metal made of gas gives out light gives out heat reflects light has plants and animals living on it Which words and phrases apply to the Earth and Moon? Which words and phrases only apply to Earth? Which words and phrases only apply to the Moon? Which words and phrases only apply to the Sun? BBC Active iposter Earth, Moon and Sun
Day and night AS3 Use these words to label the diagram correctly: Earth Sun sunlight daytime night-time Complete the sentences: 1 The Earth rotates on its 2 It takes hours to make one full rotation. 3 It rotates in an direction. 4 The part facing the Sun is in 5 The part facing away from the Sun is in anti-clockwise 24 daylight darkness axis BBC Active iposter Earth, Moon and Sun
Moon diary AS5 Monday Tuesday Wednesday Thursday Friday Saturday Sunday Keep a record of the phases of the Moon for 28 days. BBC Active iposter Earth, Moon and Sun