Astronomers observe light from a distant galaxy and notice that its spectral lines are shifted toward longer wavelengths (redshifted). What conclusion can be drawn about the galaxy from this observation?

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A The galaxy is moving directly toward Earth, and the universe is contracting.
B The galaxy is moving away from Earth, and the universe is expanding.
C The galaxy is burning out its hydrogen fuel and cooling down.
D The galaxy is rotating faster and generating stronger gravitational forces.

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Answer: B. The galaxy is moving away from Earth, and the universe is expanding.

Answer Explanation: B. Redshift occurs due to the Doppler effect when a light source moves away from the observer, stretching the light waves to longer (redder) wavelengths. The fact that almost all distant galaxies show a redshift proves they are moving away from us, providing key evidence for the expansion of the universe.

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Astronomers observe light from a distant galaxy and notice that its spectral lines are shifted toward longer wavelengths (redshifted). What conclusion can be drawn about the galaxy from this observation?

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