The Universe

• Studying the line spectra produced by hot gases and absorbed by cooler gases allows us to identify the elements in stars
• What does matter emit when its very hot?

  Light
• What does the light emitted by hot matter show when seen through a prism?

  All the wavelengths of visible light
• What is a continuous emission spectrum?

  A complete spectrum of colours showing all wavelengths of light
• What gives a continuous emission spectrum?


  A light source e.g star
• When a gas is very hot, it doesn’t emit all wavelengths of light. 
• What don't produce a continuous emission spectrum?


  Hot gases
• When does a hot gas emit certain wavelengths of light?

  To produce bright lines on a dark background
• What is a line emission spectrum?


  A series of bright lines on a dark background, produced by hot gases
• A gas cloud on its own, without a light source behind it, produces a line emission spectrum.
• What does a gas do when it's cool?

  It absorbs the same wavelength of light as it would emit when it's hot
• If a continuous spectrum travels through a cooler gas, it will ‘pull out’ or absorb certain wavelengths of light to produce a series of dark lines on a continuous spectrum of light
• What is a line absorption spectrum?


  A series of dark lines on a continuous emission spectrum. Produced by a cool gas with a hot continuous source behind it - such as a star.
• When light passes through a gas, the gas atoms may absorb certain wavelengths to produce a line absorption spectrum.
• Black hydrogen absorption lines are at the same wavelength as the bright hydrogen emission lines
• Line emission spectra are unique to a particular element
• Different elements produce different line spectra
• What are Fraunhofer lines?

  The line absorption spectrum of the sun that allows you to determine what elements are present
• What kind of lines are absorption lines?

  Dark lines
• How are absorption lines produced?

  The sun and other stars produce all wavelengths of light. As this light passes through the cooler outer atmosphere, gas atoms absorb certain wavelengths of light which produces a line absorption spectrum
• What are scientists able to do with line emission spectra?

  Compare the dark lines with the lines of known elements and identify what elements were in the cooler atmosphere
• What can wavelength of sound and light be stretched by?

  Movement
• When an object that emits waves begins to move, the movement can cause the stretching or compressing of the waves
• Whta is the Doppler shift?

  A change in wavelength and frequency caused by the relative movement of a source of waves
• Light wavelengths from an object emitting light are stretched by movement away from the observer
• What is red shift?

  When light wavelengths from an object emitting light are stretched by movement away from the observer
• What is blue shift?

  When light wavelengths from an object emitting light are compressed by movements towards the observer
• What did Hubble notice about absorption spectrum lines?

  That the lines from galaxies showed the same pattern as the Sun’s absorption spectrum showing the same elements were present, but had been shifted towards the red side of the spectrum
• Hubble realised that the red shift meant that the wavelengths of the absorption dark lines had been stretched or made longer
• What did Hubble conclude about red shift?

  The shift was caused by the galaxy moving away from us
• What is cosmological red shift?

  The shift of line absorption spectra from galaxies to the red part of the visible spectrum caused by the light passing through expanding space, which stretches the wavelengths
• Why does cosmological red shift occur?

  Due to the increasing space between the distant galaxy and the observers on earth
• What is cosmological red shift evidence of?

  The expansion of the Universe
• What did Hubble look at and realise?

  The light from galaxies further away from earth and realised that the dark absorption lines showed greater red shifts
• What did Hubble conclude?

  That distant galaxies had bigger red shifts because they were moving away faster
• Light from further galaxies has travelled for a greater amount of time through an expanding universe. This increases its wavelength, giving a greater red shift.
• The greater the distance from Earth, the bigger the red shift of the absorption lines
• What did Hubble use the red shift to calculate?

  The velocities of galaxies against their distance from Earth.
• What is Hubble’s law?

  If the distance of the galaxy away from us doubles, so does it‘s recessional velocity
• What is recessional velocity?


  The velocity away from an observer