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OCR 21st Century Science Unit P1a Revision The earth in the universe The eight planets of our Solar System 22/05/2017 Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune As well as the eight planets, the solar system is also made up of asteroids, dwarf planets, comets and moons Different Orbits 22/05/2017 Mercury = 88 days Mercury Venus Earth Mars Mars = 687 days Pluto = Jupiter 90,500 days Saturn Uranus Neptune Pluto Asteroids An “asteroid belt” lies between Mars and Jupiter. But what is an asteroid? 22/05/2017 Comets 22/05/2017 Comets are balls of dust and frozen gas. They have very elliptical orbits: Notice how the tail always points away from the sun! The Solar System summarised 22/05/2017 What makes up our solar system? Complete the following mind map with what you now about each object: The solar system Solar systems, galaxies and the Universe 22/05/2017 Our planet (around 13,000km diameter and 4500 million years old) is pretty small compared to... OUR SUN (100 times wider and 4.6 billion years old), which is small compared to… THE UNIVERSE, which contains billions of galaxies and is 14,000 million years old. THE MILKY WAY, which contains at least 200 billion stars and is 100,000 light years across, which is small compared to… How to make a solar system 22/05/2017 …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… ………………………………………………………………………………………………… Stage 1: Nebulae A nebulae is a collection of dust, gas and rock. Some examples of nebulae… 22/05/2017 Stage 2: Throw the nebula together 22/05/2017 Gravity will slowly pull these particles together… As they move inwards their gravitational potential energy is converted into heat and a big object (PROTOSTAR) or smaller objects (planets, asteroids etc) are formed Stage 3: Make a star 22/05/2017 In a star the forces of gravitational attraction pulling the particles inwards are _________ by forces acting outwards due to the huge __________ inside the star. Stars are basically ________ reactors that use _______ as a fuel. During its main sequence a star will release energy by combining hydrogen and helium nuclei (light elements) into _________ elements. Any element in space that is heavier than helium is thought to have been made in a star. Words – heavier, balanced, hydrogen, nuclear, temperatures Observing the Universe 22/05/2017 All of these methods rely on detecting radiation from stars. The Light Year 22/05/2017 Distances in space are so big that they are measured in units called “light years”: 1 light year = the distance travelled by light in one yar Q. If light travels through space (i.e. A vacuum) at 300,000 km/s how far is one light year? Because of this, when we see stars in the night sky we are actually seeing them as they were in the past. Distances in space 22/05/2017 The Sun, our closest star, is 1.6x10-5 light years away from us. The next closest star, Proxima Centauri (4.2 light years away) The centre of our galaxy, the Milky Way, is around 26,000 light years away. The Andromeda Galaxy (our closest galaxy) – approximately 2.5 million light years away Measuring distance using brightness 22/05/2017 When I look at these stars some appear brighter than others. This because they are either brighter stars or closer to me. For example, the star Antares is 10,000 times brighter than the sun but it is 500 light years away from me, so it is only the 15th brightest star in the night sky. Measuring distances to stars 22/05/2017 1) Relative Brightness The further away a star is the dimmer it is. Simple. 2) Parallax Parallax is the apparent change in position of closer stars due to the Earth moving around the sun. Distant stars Nearby star Problems in Measuring Distances 22/05/2017 1) Light pollution and other atmospheric conditions can interfere with observing stars: 2) Stars are simply very far away so the angles involved in using techniques like parallax are very small: How our Earth and the Sun compare to others… 22/05/2017 22/05/2017 22/05/2017 22/05/2017 22/05/2017 How did the universe begin? 22/05/2017 Scientists believe that the universe began by a “big bang” around 14 billion years ago: 22/05/2017 Evidence about the origins of the universe… 22/05/2017 Source of light “Spectra” 22/05/2017 If you pass the light through a gas something different is seen… helium Some wavelengths of light are absorbed by the gas – an “absorption spectrum”. If the light source is moving away the absorption spectra look a little different… 22/05/2017 Before helium helium After The absorption lines have all been “shifted” towards the longer wavelength end (red end)… This is called red shift. The faster the light source moves the further its light will be “shifted” Before After A similar effect happens with sound – this is called “The Doppler Effect” 22/05/2017 Red Shift simplified 22/05/2017 Basically, if I walk towards you I’ll look slightly more blue. Then, if I walk away from you, I’ll look slightly more red!! Let’s try it… 22/05/2017 22/05/2017 22/05/2017 Light from different stars and from the edge of the universe also shows this “red-shift”. This suggests that everything in the universe is moving away from a single point. This is the BIG BANG theory Red shift summary 22/05/2017 Light from other galaxies has a longer _________ than expected. This shows that these galaxies are moving ____ from us very quickly. This effect is seen to a greater extent in galaxies that are _______ away from us. This indicates that the further away the galaxy is, the ______ it is moving. This evidence seems to suggest that everything in the universe is moving away from a single point, and that this process started around 15 _____ years ago. This is the ____ ________ Theory. Words to use – faster, away, big bang, billion, wavelength, further Hubble’s Law 22/05/2017 The speed at which galaxies are moving away from us is proportional to their distance from us. In other words, the further away they are, the faster they go. Edwin Hubble 1889-1953 Big Bang Theory 22/05/2017 Some scientists have explained that red shift can actually be used to support the Big Bang Theory – this explanation is based around the rates of expansion and contraction of different galaxies. If our neighbouring galaxy is expanding at a different rate to the Milky Way then it will appear red or blue-shifted. So Mr President, red shift shows us that galaxies are moving and therefore we assume that space itself is expanding. Elementary! Stephen Hawking, 1942 - 22/05/2017 The end of the Universe 22/05/2017 There are some theories about how the universe will end but its difficult to tell due to difficulties in measuring objects that are so far away: “The big crunch” – if there is too much mass (i.e. too much matter) the universe will collapse under its own gravity. It may then do another “big bang” – this is the “oscillating universe” theory. “Expanding Universe” – if there isn’t enough mass in the universe then it will just keep on expending forever. If there is just the right mass in the universe then it will reach a fixed size. The End of the Universe 22/05/2017 Basically, how the universe will end depends on its “energy-mass density”. Size of universe Stephen Hawking Now Open universe Critical density Closed universe Time