Author Question: When an astronomer measures the redshift to a distant galaxy, exactly what physical process is being ... (Read 84 times)

09madisonrousseau09 · **on:** Jul 27, 2018

When an astronomer measures the redshift to a distant galaxy, exactly what physical process is being measured?

What will be an ideal response?

Question 2

The spectral classification of stars started with the amount of hydrogen present in their spectra, but a better method now uses the amount of oxygen in the star's spectra.

a. True
b. False
Indicate whether the statement is true or false

wuly · **Reply #1 on:** Jul 27, 2018

Answer to Question 1

Galaxies are being separated from each other as space-time expands. As it expands, photons travelling through space are stretched so that their wavelength increases. Photons from distant sources spend more time travelling through space and are stretched more. Therefore, when an astronomer measures the redshift to a distant galaxy, he or she is measuring the spectra to their apparent brightness. When a galaxy is moving away from the observer, their spectrum has shifted to longer (red) wavelengths.

Answer to Question 2

False