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The Universe
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The Universe


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Year 10 The Universe - For additional resources visit:

Year 10 The Universe - For additional resources visit:

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  • 1. Hubble Space Telescope The Universe Sarah Jones
  • 2. Hubble Space Telescope
  • 3. "It must be a strange world not being a scientist, going through life not knowing - or maybe not caring - about where the air came from, and where the stars at night came from, or how far they are from us. I want to know." Michio Kaku
  • 4. Hubble Space Telescope
  • 5. Hubble Space Telescope
  • 6. Ancient astronomers believed the universe was made up of about 3000 stars, the moon and the sun and these objects revolved around the earth. We now know that the earth is not the centre of the universe and that the sun is only one of millions and millions of stars.
  • 7. Claudius Ptolemy’s earth-centered model of the universe
  • 8. Constellations Many stars that we can see form recognisable patterns. The stars in a constellation keep the same shape but may only appear on summer or winter nights due to the Earth’s revolution.
  • 9.
  • 10.
  • 11. Star Distances The distances to the stars are enormous with vast spaces between them. Our sun is the closest star being 150 000 000 km away. The next closest star is 41 000 000 000 000 km away or 270 000 times the distance of the sun.
  • 12. The distances to the stars are far too large to measure in kilometres. Instead we use the astronomical unit of distance called the light- year. This is the distance light travels in one year. Light travels at about 300 000 000 metres per second (3×108 m/s). So in one year light travels about 9 500 000 000 000 km.
  • 13. • A parsec (pc) is another commonly used astronomical unit of length – it is equivalent of 3.26 light-years. • The parsec is based on the phenomenon known as parallax.
  • 14. When you look at the stars you are actually looking back in time. The closest star in the Southern Cross is 220 light years away. This means the light left this star 220 years ago (i.e. as the star was in 1788). Science World 10
  • 15. Naming Stars The stars in the sky have been given names according to their brightness. The brightest star is called the alpha star (α-star), the second brightest the beta star (β-star), then gamma (γ- star), delta (δ-star) and so on.
  • 16. In the Southern Cross, the brightest star is called the α-Crucis. The Pointers are located nearby and this constellation is known as Centaurus. The brighter of the 2 stars is known as α- Centauri (closest star to Earth apart from the Sun) and the second star is known as β-Centauri.
  • 17. Movement of Stars The stars appear to move across the sky. This movement is caused by the west to east rotation of the earth. Science World 10
  • 18. Stars are made of …? Stars are gaseous objects in space that give off light and heat. Our sun is composed of: 80% H 19% He 1% trace elements
  • 19. The enormous size of a star creates huge gravitational forces which squeeze the atoms of the gases together and creates immense pressure and heat. At this temperature, electrons are stripped from the atoms, leaving positively charged nuclei which are in constant rapid motion.
  • 20. NASA/SDO/GoddardSpaceFlightCenter
  • 21. Plasma a state of matter, different from solids, liquids and gases, which exist in the extreme heat in the interior of stars (conducts electricity and generates a magnetic field). Nuclear Fusion is when H nuclei fuse together to form He and release large amounts of energy (occurs in the core of the sun).
  • 22. Einstein proposed: In the fusion reaction in the sun, 655 million tons of H is converted to 650 million tons of He every second. The 5 million tons of H used up releases 4.5 x 1026 J/s. This is the same amount of energy that all power stations in Australia could produce in 7 billion years.
  • 23. Structure of the Sun Science World 10
  • 24. Light From Stars • Brightness and colour of a star are important in determining its size and life expectancy. • Astronomers refer to a stars brightness as its magnitude. • The colour of a star is due to its temperature.
  • 25. Brightness and Colour of Stars
  • 26. Apparent Magnitude • The brightness of a star when viewed from Earth. • As the brightness of a star decreases the apparent magnitude becomes more positive. i.e. Stars just visible with the naked eye have a magnitude of about 6. Sirius, the brightest star in the sky, has a magnitude of – 1.4.
  • 27. Apparent magnitude is not a measure of the star’s actual brightness because a very bright star could be so far away from earth that it appears dim.
  • 28. Absolute Magnitude • Measures the actual brightness of a star by comparing the amount of light given off by that star if it was a set distance from earth. • The amount of light given off is determined by its size (amount of matter).
  • 29. Science World 10
  • 30. Colour • Hottest stars (e.g. Rigel) – white to blue light • Coolest stars – red light • Very hot stars (Rigel) give off large amounts of UV (ultraviolet) light which our eyes cannot detect. Appears as blue. • Astronomers are able to calculate the surface temperature of stars by measuring the wavelength (λ) of light given off.
  • 31. Relationship – Brightness and Colour • If two stars are the same colour, they must have the same surface temperature. • If the absolute brightness is larger, then star is larger. • If a red and a blue star are the same size they will have the same brightness, but the blue star will radiate more energy/second because it is hotter.
  • 32. Binary Stars • Two stars that revolve around each other. • There have been nearly 700 000 binaries observed by astronomers. • Two famous binaries in the Southern Hemisphere are Alpha-Centauri (brightest star of the Pointers) and Alpha-Crucis (star at the foot of the Cross).
  • 33. Star Life Cycles • Stars are born in clouds of gas (mainly hydrogen) and dust that occur throughout the universe. Occasionally one of these clouds collapses on itself, becoming hotter and denser as the gravitational force increases. This is the embryonic stage in the life of a star – Protostar. • Eventually the gas becomes hot enough to start nuclear fusion reactions and the star begins to grow.
  • 34. Nebula – massive cloud of gas and dust.
  • 35. Supernova – a spectacular explosion which ends the life of a star.
  • 36. Birth and Death of Stars • The life cycle of a star depends entirely on its mass. • A protostar with a mass less than 0.1 of the mass of the sun will continue to shrink but will never get hot enough for nuclear reactions to begin. It will fade to form a small red star before turning cold and dying.
  • 37. A star about the size of our sun initially glows very brightly. It then settles down to a long stable middle-life period of about 10 billion years. As the star ages and its hydrogen is used up, its surface temperature decreases. Finally, when little hydrogen remains, the stars core shrinks, the outer layers expand and cool and the star forms a red giant.
  • 38. Gases in the outer regions then drift into space and the remaining gases collapse into a small, very dense object known as a white dwarf. These stars are very small. Eventually the white dwarf cools down and fades away.
  • 39. Stars 2-6 times the size of the sun have much shorter but spectacular lives. These stars only live for about 1 million years. The mass in large stars create enormous gravitational forces in the core of the star. The nuclear reactions use fuel very rapidly, creating very bright stars (blue). When the fuel runs out there is a tremendous outburst of energy – Supernova. The star’s matter is blown into space, leaving a nebula. When this explosion occurs the brightness of the star increases a billion times.
  • 40. Science World 10
  • 41. HR Diagram One of the most useful and powerful plots in astrophysics is the Hertzsprung-Russell diagram (H-R diagram). It originated in 1911 when the Danish astronomer, Ejnar Hertzsprung, plotted the absolute magnitude of stars against their colour (hence effective temperature).
  • 42.
  • 43. Nebulas and Neutron Stars • A supernova occurs about once every 75 years in our galaxy. • Some nebulas emit their own light and glow like stars. They can glow pink, blue green or yellow depending on the type of gas in the cloud. E.g. Great Nebula of Orion. • Other nebulas do not glow and black out the light from the stars behind them. E.g. The Horsehead Nebula. This is a dark nebula which can be seen against the glow of stars in the background.
  • 44. Horsehead Nebula
  • 45. A Neutron star is an incredibly dense star less than 20km in diameter formed during a supernova explosion. The remainder of the star’s core is pulled inwards by immense gravitational forces. They are so small that they do not glow very brightly but send out pulsating radio signals. They can be called pulsars.
  • 46. Black Holes • Invisible objects in space that emit X-rays and that are thought to form when the most massive stars explode. • After the supernova explosion the core collapses on itself, and unlike a neutron star, these massive stars (10 times size of sun) keep on collapsing. • The gravitational force that is created is so strong it will not even allow light to escape.
  • 47. Galaxies • The Milky Way is just one of billions of galaxies in the observable universe. • It is estimated to contain between 200 and 400 billion star.
  • 48. Edwin Hubble Astronomer Edwin Hubble revolutionised the field of astrophysics. His research helped prove that the universe is expanding, and he created a classification system for galaxies that has been used for several decades.
  • 49. Spiral Galaxy
  • 50. Barred Spiral Galaxy
  • 51. Elliptical Galaxy
  • 52. Irregular Galaxy
  • 53.
  • 54. Origin of the Universe • Cosmology is the study of the origin and structure of the universe. • Two models describing the origin of the universe:
  • 55. The Steady State Model • This model proposes that the universe has always existed. The universe is infinitely old, it has no birth date and will never end. The universe is endless in time and space. This model accounts for the fact that stars and galaxies die and re- form. • This model avoids the difficult question of how the universe was created. There are few supporters of this model because recent astronomical evidence does not fit it at all.
  • 56. The Big Bang Model This model suggests that the universe began as a massive explosion; it is based on evidence that the universe is expanding. About 10 billion years ago all matter in the universe was contained in a hot, dense ball of radiation and sub-atomic particles. An explosion took place and the matter expanded. As it expanded it cooled and electrons, protons and neutrons formed. On further expansion and cooling, small gaseous atoms like hydrogen and helium formed, then larger ones. Where the exploded matter was denser, gravitational forces squeezed particles of matter together to from galaxies containing stars.
  • 57.
  • 58. Red Shift Astronomers have found that the wavelength of the light (measured with a spectrometer) coming from most stars has shifted towards the red end of the spectrum. This occurs when stars are moving rapidly away from earth. This is considered evidence that the universe is expanding.
  • 59.
  • 60. Cosmic microwave background radiation
  • 61. The Future of the Universe • What will happen to the expanding universe? There are two theories.
  • 62. The universe will go on expanding forever. The universe will eventually die as the stars and galaxies are reduced to clouds of gas and dust.
  • 63. The ‘Big Crunch’ suggests that the universe will expand to a certain point and then collapse back on itself in a reversal of the Big Bang. This will once again form a hot, dense ball of matter that will start a second Big Bang and a new universe will be born containing all the matter that was in the previous universe.