How can we measure a galaxy's velocity via a star?

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SUMMARY

This discussion clarifies the method of measuring a galaxy's velocity through the spectrum of a star. The key point is that the star used for comparison is located within our galaxy, serving as a reference point or "laboratory" for spectral analysis. To determine redshift or blueshift, one must compare the absorption lines of the galaxy's spectrum to those obtained from laboratory measurements, rather than to the spectrum of the nearby star. This distinction is crucial for accurate velocity measurements of distant galaxies.

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  • Understanding of spectral analysis techniques
  • Familiarity with redshift and blueshift concepts
  • Knowledge of absorption lines in spectroscopy
  • Basic principles of astrophysics and galaxy dynamics
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  • Learn about redshift and blueshift calculations in cosmology
  • Study the significance of absorption lines in stellar spectroscopy
  • Explore laboratory methods for measuring spectral lines
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Astronomers, astrophysics students, and anyone interested in the methods of measuring cosmic velocities and understanding spectral data analysis.

Phys12
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In this video (), we first took the spectrum of a star and then of a galaxy which look like the following:

Capture.jpg

However, what I don't get is: if we take the spectrum of a star and then of the galaxy the star is in, shouldn't it give me the same spectrum as they're moving in the same speed? And if we want to determine the redshift/blueshift, shouldn't we look at the absorption lines and compare them to the ones we get in our laboratories rather than a star itself?

Thanks!
 
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The star is in our galaxy, not in the galaxy whose redshift you are measuring. So the star is nearby and is basically "the laboratory".
 
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phyzguy said:
The star is in our galaxy, not in the galaxy whose redshift you are measuring. So the star is nearby and is basically "the laboratory".
Oh, got it, thanks! :)
 

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