Which astronomer demonstrated that the redshift of galaxies increases with distance, implying expansion?

• A. Galileo
• B. Hubble
• C. Copernicus
• D. Kepler

Answer: (B)

The key idea being tested is that a galaxy’s redshift grows with its distance, pointing to the expansion of the universe. Edwin Hubble established this by measuring distances to galaxies (using standard candles like Cepheid variables) and comparing those distances to the galaxies’ redshifts from their spectra. He found that galaxies farther away have larger redshifts, meaning they are receding faster. This linear relationship, now known as Hubble’s law, shows that space itself is expanding. The other astronomers listed—Galileo, Copernicus, and Kepler—made foundational contributions to astronomy and planetary motion, but none demonstrated this redshift–distance relationship or concluded that the universe is expanding.