• Question: Galaxies look stationary, so why do scientists say that they rotate?

    Asked by Mason The Amazing :) to Andrew, Hina, Ian, Kathryn, Leah-Nani, Xu on 14 Jun 2018.
    • Photo: Kathryn Burrows

      Kathryn Burrows answered on 14 Jun 2018:

      Good question, I was not sure myself so I found this link: https://astronomy.stackexchange.com/questions/300/what-is-the-evidence-that-galaxies-rotate?utm_medium=organic&utm_source=google_rich_qa&utm_campaign=google_rich_qa

      It seems they can look at the atomic spectra lines and see doppler shifting which indicates rotation [let me know if you want this explained!]. Also the spiraling arms photographed are an indication.

    • Photo: Andrew Margetts-Kelly

      Andrew Margetts-Kelly answered on 15 Jun 2018:

      The stars in a galaxy must be orbiting each other in the galaxy otherwise they will all fall into each other leaving a supermassive black hole. To be able to find out how fast the stars are moving in a galaxy we look at the light they emit.
      We look at the colour of light coming from the different bits of the galaxy. The bits moving away from us will look like they have a longer wavelength than they should have and the bits that are moving towards us will look like they have a shorter wavelength then they should have. By comparing the difference in the wavelength of light coming from either side of the galaxy we can tell how fast a galaxy is rotating.

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