How do we know which way galaxies are moving?

Astronomers and scientists can figure out which galaxies are moving towards us and away from us, I'd like to know how such conclusions are drawn...

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  • 9 years ago
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    One shift

    Two shift

    Redshift

    Blueshift

    Source(s): Apologies to Dr. Seuss.
  • 9 years ago

    Every such (self-) luminiscent object can be analysed spectroscopically. It reveals (emission) lines, that were studied for the last two centuries in Earth bound laboratories. Every Physics major student has done that in the lab.

    These lines that are so fixed have been observed to shift (in frequency/wavelength) towards 'Red' side (longer wavelength/lower frequency) if the body is moving away from us; or towards 'Blue' end (shorter wavelength/higher frequency) if it is moving towards us. It is called 'Doppler' shift.

  • Anonymous
    9 years ago

    We can tell their moving by the red hue given to everything in the universe. This tells us that it's moving rapidly. Because it's moving so rapidly over X amount of years (Depending on the galaxy) we can tell which galaxy's are getting brighter/getting bigger at a faster rate than others.

    Another fact: everything is moving at such a speed that it is all rapidly expanding. Everything on Earth is expanding as well.

    Why don't we notice this?

    Because we are expanding at the same rate as earth and everything on it.

  • The measure the frequency of the light, know as the red shift.

    Think of a sound like a siren, as it gets closer it sounds on tone, then as it passes it sounds another. Light is exactly the same.

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  • Anonymous
    9 years ago

    In the spectrum, light is red shifted for objects moving away, and blue shifted for approaching objects.

    The analogy is like a train whistle which is higher pitched when it is approaching you and when the train passes you and moves away, the train whistle drops in frequency as it passes you.Tell me you have heard that! It is the same as racing cars' engines as they approach and pass people in the stands.

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