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      Lesson details

      Learning outcome

      I can describe what redshift is and how it is measured.

      Key learning points

      1. Telescopes extended what was visible after their invention in the seventeenth century.
      2. Images detected by telescopes in space are not distorted by effects of the Earth’s atmosphere.
      3. A galaxy is a group of hundreds of billions of stars, and there are many galaxies spread across the universe.
      4. A visible spectrum of light emitted from stars or galaxies shows dark lines of frequencies of light.
      5. Red shift is the movement of hydrogen lines towards the red end of the visible spectrum.

      Keywords

      • Space telescope - is a telescope positioned in space to avoid atmospheric interference and observe parts of the spectrum which cannot reach the Earth’s surface

      • Galaxy - is a collection of many millions or billions of stars held together by gravitational forces

      • Redshift - is the increase in the wavelength of light (and decrease in its frequency) cause by the movement of a star or galaxy away from us

      Common misconception

      Stars twinkle (change brightness rapidly).

      Explore the ideas that Earth’s atmosphere is made of moving air that refracts light from stars in changing directions to distort the light coming from stars.

      Teacher tip

      This lesson goes beyond the syllabus in places in order to provide pupils with an understanding of redshift, which is necessary for understanding the big bang theory for the origin of the universe.

      Licence

      This content is © Oak National Academy Limited (2025), licensed on Open Government Licence version 3.0
      except where otherwise stated. See Oak's terms & conditions
      (Collection 2).

      Lesson video

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      Prior knowledge starter quiz

      6 Questions

      Q1.
      A star fuses hydrogen in its core. It is stable for long periods of time (often billions of years).

      Correct Answer: main sequence

      Q2.
      What type of star will the Sun change into next, after it stops fusing hydrogen in its core (in about 5 000 000 000 years)?

      red dwarf star
      white dwarf star
      Correct answer: red giant star
      white dwarf star

      Q3.
      Sort the following stages of a star's life, for a star similar in size to the Sun, into the order in which they take place.

      1 - nebula
      2 - protostar
      3 - main sequence star
      4 - red giant star
      5 - white dwarf star
      6 - black dwarf star

      Q4.
      What is a giant exploding star called?

      Correct Answer: supernova, a supernova, super nova, a super nova

      Q5.
      What is a neutron star that is formed from the core of a supernova?

      a very large and hot white dwarf star
      an incredibly hot ball of plasma and gas
      an incredibly dense ball of atoms
      Correct answer: an incredibly dense ball of neutrons

      Q6.
      What is a black hole that is formed from the core of a particularly large supernova?

      the core of a massive star compressed to a few thousand metres across
      the core of a massive star compressed to a few hundred metres across
      the core of a massive star compressed to a few metres across
      Correct answer: the core of a massive star compressed to almost no size at all

      6 Questions

      Q1.
      Which of the following optical instruments can improve what we can see in space?

      Correct answer: binoculars
      microscopes
      stethoscopes
      Correct answer: telescopes

      Q2.
      What makes a star appear to twinkle in the night sky?

      clouds
      Correct answer: moving air
      gases around the star
      nebulae in space

      Q3.
      What are the advantages of using a space telescope compared to a telescope on Earth?

      It is very expensive to construct and launch.
      Correct answer: It encounters no atmospheric distortion.
      Correct answer: It can detect more types of radiation.
      It is smaller in size.

      Q4.
      How do Messier objects that can be seen with a telescope differ in appearance from stars?

      They are much brighter.
      They have distinct colours.
      Correct answer: They don't have sharp outlines.
      Their brightness varies in a regular pattern.

      Q5.
      What are absorption lines in a spectrum of light from a star?

      coloured lines that add together to make a visible spectrum
      black lines on a visible spectrum caused by a telescope
      Correct answer: black lines on a visible spectrum caused by gases around a star
      black lines on a visible spectrum caused by air in Earth's atmosphere

      Q6.
      What observation shows that redshift has occurred and that the wavelength of light from a distance galaxy has increased?

      there is less red light in the visible spectrum of the galaxy
      there is more red light in the visible spectrum of the galaxy
      Correct answer: absorption lines in its spectrum have lower than expected frequencies
      absorption lines in its spectrum have higher than expected frequencies

      To help you plan your 11 physics lesson on: Observing the universe, download all teaching resources for free and adapt to suit your pupils' needs...