Astronomy - Chapter 4 - Galaxies and Cosmology

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  • Created on: 10-04-13 14:49
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  • Astronomy - Chapter 4 - Galaxies and Cosmology - The Milky Way
    • General Facts
      • There are 200 million stars that make up our galaxy - The Milky Way
      • Our solar system is in the 'arm' of Orion
      • Looking at the Milky Way with the naked eye would be a VERY clear night you would see a *****/band of the colour pink
      • With the aid of a telescope you can see in detail some stars in the band/'arm'
      • With the aid of binoculars you can see a few couple hundred of stars in the band
      • To the naked eye the Milky Way has a milky appearance hence the name 'Milky'
    • The Milky Way
      • There are 3 main components of our galaxy
        • The DISC: containing young stars, gas, dust and sites of star formation in four major spiral arms
        • The BULGE: surrounding the NUCLEUS - astronomers now believe that there is a massive black hole at the centre
        • A HALO: containing GLOBULAR CLUSTERS - dense groups of relatively old stars
      • The arms contain huge clouds of gas and dust that are opaque to visible light
    • Using 21 cm radio waves
      • When the hydrogen atom absorbs energy and the electron is excited to a higher quantum level, a spectral absorption line is produced – in the case of neutral hydrogen, there is only one spectral line and this is at 21cm wavelength
      • Visible light can pass through many parts of the Milky Way. However, the material found in our galaxy is mostly formed from hydrogen
        • Hydrogen atoms are neutral - there is one electron and one proton
      • This waveband is in a radio frequency and so astronomers study the nature of our galaxy by radio astronomy. Another bonus for astronomers is that this waveband is able to pass unaffected through the Earth’s atmosphere.


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