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Astronomy & space · Advanced university

Scale factor from cosmological redshift

Apply the homogeneous expanding-universe cosmological-redshift model, not a local Doppler shift.

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Method and conditions

Apply the homogeneous expanding-universe cosmological-redshift model, not a local Doppler shift.

aemit/anow = 1/(1+z)

Worked examples

In a cosmological expansion model, a source has redshift 5.4. Find aemit/anow. Round the final result to 4 decimal places if needed.

The ratio is the reciprocal of 1+5.4.

0.1563

In a cosmological expansion model, a source has redshift 1.3. Find aemit/anow. Round the final result to 4 decimal places if needed.

The ratio is the reciprocal of 1+1.3.

0.4348

Try it

  1. In a cosmological expansion model, a source has redshift 8.1. Find aemit/anow. Round the final result to 4 decimal places if needed.

  2. In a cosmological expansion model, a source has redshift 9. Find aemit/anow. Round the final result to 4 decimal places if needed.

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Answers and marking notes
  1. 0.1099

    The ratio is the reciprocal of 1+8.1.

  2. 0.1

    The ratio is the reciprocal of 1+9.

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