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Astronomy & space · Advanced university

Redshift from a spectral line

This measured wavelength ratio alone does not select a velocity-distance model.

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Method and conditions

This measured wavelength ratio alone does not select a velocity-distance model.

z = λobs/λrest − 1

Worked examples

A model line has rest wavelength 590 nm and observed wavelength 3481 nm. Find redshift z. Round the final result to 4 decimal places if needed.

Use z=λobs/λrest−1 = 3481/590−1.

4.9

A model line has rest wavelength 550 nm and observed wavelength 1870 nm. Find redshift z. Round the final result to 4 decimal places if needed.

Use z=λobs/λrest−1 = 1870/550−1.

2.4

Try it

  1. A model line has rest wavelength 480 nm and observed wavelength 3072 nm. Find redshift z. Round the final result to 4 decimal places if needed.

  2. A model line has rest wavelength 890 nm and observed wavelength 5696 nm. Find redshift z. Round the final result to 4 decimal places if needed.

Check your work

Answers and marking notes
  1. 5.4

    Use z=λobs/λrest−1 = 3072/480−1.

  2. 5.4

    Use z=λobs/λrest−1 = 5696/890−1.

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