Topic 7 Astronomy

• The gravitational field strength on the surface of a body depends on the mass of the body and its radius. The greater its mass and smaller its radius the greater its surface of gravity
• Our Solar System consists of the sun(our star), eight planets and their natural satellites (such as our moon), dwarf planets, asteroids and comets
• My (Mercury), Very (Venus), Easy (Earth), Method (Mars), Just (Jupiter), So (Saturn), U (Uranus), Name (Neptune), Planets (Pluto which is a dwarf planet now)
• One of the best known models of our solar system was the geocentric model, which said that the earth was in the centre of everything with the planets and the sun orbiting around it - made by Ptolemy (c100 - 170)
• A polish astronomer disproved the Geocentric model, and made up his own the heliocentric model with the sun at the centre of the solar system (Helios god of sun)
• All planets, dwarf planets, comets and asteroids move in elliptical orbits around the sun. Many of the planets also have natural satellites orbiting around them
• For circular orbits, the force of gravity can lead to changing velocity but unchanged speed due to its direction constantly changing
• for a stable orbit the radius must change if orbital speed changes
• Telescopes in orbit around the earth give much clearer images than ground-based telescopes
• Many objects emit radio waves and infrared radiation, different types of telescopes are made to detect different types of EM waves
• If the radius of the orbit decreases, the speed increases as the gravitational attraction is much greater
• Big bang theory states that the whole universe and all the matter in it started out as a tiny point of concentrated energy. The universe expanded from this point and is still expanding. As it expanded gravity caused matter to clump together to form stars
• The Steady State theory suggests that the universe has always existed and is expanding and that new matter is continuously created within the universe as it expands
• the Big Bang theory states that huge amounts of radiation were released at the beginning of the universe, because the universe is expanding the wavelength of this has increased. It is called Cosmic Microwave Background Radiation
• both the steady state and big bang theory say the universe is expanding
• observations of red-shift in the light from other galaxies can be used to support both theories. because both say the universe is expanding.
• There is more evidence supporting the Big Bang theory than the Steady State theory, it is the currently accepted model for the origin of the Universe
• The pitch of a sound depends on frequency. If a wave source is moving relative to an observer there will be a change in the observed frequency and wavelength. As an emergency vehicles siren travels away from you its pitch gets lower (longer wavelength)

  
• The visible spectrum of light from stars contains patterns of dark lines. If these are red shifted (moved towards the red end of the spectrum) the star is moving away from us and the further the lines are shifted the faster the star is moving relative to us

  
• If a star is moving towards us the wavelength and frequency of the light waves become shorter and so the pattern of lines moves towards the blue ends of the spectrum
• Red Shift is a result of the space between the Earth and the galaxies expanding. This expansion has the effect of increasing the wavelength of the light from these galaxies, shifting them towards the red end of the spectrum. The more red-shifted the light from a galaxy is, the faster the galaxy is moving away from Earth.
• both the Big Bang and Steady State theories of the origin of the Universe both account for red-shift of galaxies because they both state that the universe is expanding
• The discovery of CMB radiation led to the Big Bang theory becoming the currently accepted model because the Steady state theory couldn't provide evidence for this
• First part of a life cycle of a star : A nebula is a cloud of dust and gases, these are pulled together by their own gravity. As it contracts it becomes denser and hotter. As more mass is attracted the clouds gravitational pull gets stronger. A protostar is formed
• Second part of a life cycle of a star: After the protostar is formed, eventually the temperatures and pressures in the centre of he protostar become high enough to force hydrogen nuclei to fuse together and form helium.
• Third part of a life cycle of a star: The main sequence star is formed, when they have fused most of their hydrogen into helium, the core is not hot enough to withstand gravity and collapses. The outer layers expand to form a Red Giant
• Fourth part of a life cycle of a star: The star remains as a red giant for about a billion years, the rest of the star after the shell of gas is removed collapses to form a white dwarf star. It gradually cools to become a black dwarf
• how does the balance between thermal expansion and gravity affect the life cycle of stars?pressure from hot gases pushed the star outwards, and gravity pulls it inwards. if the pressure from the hot gases is stronger than the gravity, the star will expand. if it is weaker than the gravity, the star will contract.
• stars with considerably more mass than the sun are hotter and brighter. They fuse hydrogen into helium faster becoming red supergiants. the star rapidly collapses then explodes into a supernova. If what is left is 4 or more times the size of the sun, gravity pulls the remains together to form a black hole. If the remains are not massive enough to form a black hole gravity pulls them together to form a small, dense star called a neutron star
• The invention of photography allowed astronomers to make more detailed observations and measurements than what was possible before and computers further increased this.
• telescopes in orbit around the earth give much clearer images than ground based telescopes since clouds and dust in the air dont interfere with images.
• The solar system investigated using space probes
• Artificial Satellites: Man-made satellites that have been sent into space for purposes such as satellite imaging and communications
• Natural Satellites: The moons that orbit planets