Which observation supports that the universe is expanding?

• A. Blue Shift of Nearby Stars
• B. Parallax of Distant Galaxies
• C. Redshift of Distant Galaxies
• D. Occultation of Planets

Answer: (C)

The key idea is that light from distant galaxies reveals how fast they are receding, which points to the expansion of the universe. Light stretches as space itself expands, so distant galaxies show redshift—their photons shift to longer wavelengths. The more distant a galaxy, the greater its redshift, aligning with what we observe as the universe expanding (Hubble’s relation). Blue shift would mean objects are moving toward us, not a universal expansion signal. Parallax measures distance within our neighborhood and doesn’t demonstrate expansion, and occultation occurs when one object passes in front of another, which isn’t about cosmic growth.