Which observation provides evidence that galaxies are moving away from Earth?

Which observation provides evidence that galaxies are moving away from Earth?

• A. Red Shift
• B. Blue Shift
• C. Parallax
• D. Cosmic Microwave Background

Answer: (A)

Redshift is observed when light from a galaxy has its wavelengths stretched toward the red end of the spectrum. This happens when the galaxy is moving away from Earth along our line of sight, or when the fabric of space itself expands between us and the galaxy. By measuring how much the spectral lines are shifted, we can determine the recessional velocity of the galaxy, and this pattern—more distant galaxies receding faster—fits with the expansion of the universe described by Hubble's law. Blue shift would mean the galaxy is moving toward us, which is not the general case for distant galaxies. Parallax is a method for estimating distance based on Earth's motion, not the motion of galaxies away from us. The cosmic microwave background is the leftover radiation from the early universe and supports the idea of an expanding cosmos, but it doesn’t show the specific motion of individual galaxies relative to Earth. Thus, redshift in spectral lines provides the clearest evidence that galaxies are moving away.

Redshift is observed when light from a galaxy has its wavelengths stretched toward the red end of the spectrum. This happens when the galaxy is moving away from Earth along our line of sight, or when the fabric of space itself expands between us and the galaxy. By measuring how much the spectral lines are shifted, we can determine the recessional velocity of the galaxy, and this pattern—more distant galaxies receding faster—fits with the expansion of the universe described by Hubble's law.

Blue shift would mean the galaxy is moving toward us, which is not the general case for distant galaxies. Parallax is a method for estimating distance based on Earth's motion, not the motion of galaxies away from us. The cosmic microwave background is the leftover radiation from the early universe and supports the idea of an expanding cosmos, but it doesn’t show the specific motion of individual galaxies relative to Earth. Thus, redshift in spectral lines provides the clearest evidence that galaxies are moving away.