Redshift describes which phenomenon in astronomy?

• A. The apparent decrease in wavelength of light from stars moving away from Earth.
• B. The apparent increase, or lengthening, in the wavelength of light from stars moving away from Earth.
• C. The rate at which stars move across the sky
• D. The brightness of a star as seen from Earth

Answer: (B)

Redshift is about light wavelengths stretching as objects move away. When a star or galaxy is receding, its light waves are spaced farther apart, so the spectral lines shift toward longer wavelengths, the red end of the spectrum. This Doppler effect for light is why distant objects show a redshift. It’s not about how fast an object moves across the sky (that’s relative motion on the celestial sphere) or about how bright the object appears. Blueshift would occur if an object were moving toward us, shortening the wavelengths toward the blue end.