P7.3

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  • Created by: amy_mair
  • Created on: 23-06-16 17:00
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  • P7.3
    • Astronomial Distances
      • Parallax
        • 1. Parallax is an apparent change in position of an object against a distant background
          • It makes stars appear to move relative to distant ones over the course of the year
          • The parallax angle is half the angle moved against the distant backgrounds stars over 6 months. The nearer an object is to you, the greater the angle
        • 2. The angle is often measured in arcseconds rather than degrees
          • 1 arcsecond = 1- (1 / 3600)
        • 3. Parallax is useful for calculating the distance to nearby stars. It is a similar magnitude to a light year
        • Astronomers usually use a distance called parsec
        • You can calculate the distance to a star using the equation
          • Distance = (1/ angle)
      • Intensity
        • 1. The luminosity or intrinsic brightness of a star depends on the time and the temperature.. The bigger and hotter it is, the more energy it gives out, so the brighter it is
        • 2. As you move away from a star, it looks dimmer- because the energy reaching you get less. So the observed intensity of the light seen on earth depends on luminosity and how far it is away from earth
        • 3. So if you looked at 2 stars with the same luminosity but one was further away than the other, the more distant star will look dimmer
      • Cehied Variable
        • 1. A group of stars called the Cephied Variable pulse in brightness- they get brighter and then dimmer over a period of several days
        • 2. How quickly they pulse is directly linked to their luminosity. The greater the luminosity the longer time between the pulse
        • 3. So, if you see 2 Cepheid variable stars with the same observed brightness that pulse at different rates, you know that the star with the longer pulse period must have the higher luminosity
    • The scale of the universe
      • Telescopes
        • 1. If you went out in the countryside on a clear night you could probably see about 1500 stars. If you looked with a small telescope, you could probably see half a million
        • 2. The more stars you can see, the more you notice that they are not evenly dotted about the sky.
          • Most of the stars appear to be concentrated in a bright strip across the sky - the milky way galaxy
        • 3. Away from the strip, the number of visible stars is much smaller
        • 4. Our sun is jut one of the approximately 10 to the 11th star in the galaxy
        • 5. The milky way is actually a spiral galaxy. But because we are part of its disk, we can see it edge on
        • The Curtis Shapley Debate
          • Shapleys argument
            • 1. Shapley believed the universe was just one gigantic galaxy about 100,000 parsecs across
            • 2. He reckoned our sun and solar system were far from the centre of the galaxy
            • 3. He believed that nebulae were huge clouds of gas and dust. These clouds were relatively nearby and actually a part of the milky way
          • Structure of the universe
          • Curtis's argument
            • 1. Curtis thought the universe was made up of many galaxys
            • 2. He thought our galaxy was smaller than shapley suggested
            • 3. The spiral nebulae were other very distant galaxies, completly separate from the milky way
          • Both of them were right
            • 1. Shapley was right that the solar system is far from the centre of our galaxy
            • 2. Curtis was also right about the spiral nebulae
    • The scale of the Universe
      • Hubble
        • 1. Hubble helped solve the Curtis-Shapley debate with the observations of the Andromeda Nebula
        • 2. Using images taken using the largest telescope at the time, he found that this spiral shaped fuzzy blob, some of whihc were Chepeid Variables
        • 3. Hubble calculated the distance to the Andromeda Nebula by working out the distance to the Cepheid Variables within it, using the relationship between their brightness and pulse frequency
        • He studied other spiral nebulae and found a similar result
      • Red Shift
        • Distant galaxies are moving away from us
        • 1. When a galaxy is moving away from us the wavelength of the light from it changes- the light becomes redder. This is called red shift
        • By seeing how much the light has been redshifted you can work out the recession velocity of the galaxy
        • Using red shift Hubble found this... The more distant a galaxy the faster it is moving away from us
        • This suggests that the universe is expanding
        • Rd shift is fairly to measure, so a galaxy recession velopsicy can be calculated easily enough
          • Speed of recession = hubble's constant x distance
        • Using data on Cephied variables stars from distant galaxies has givven us better values of Hubbles constant

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