✔ 最佳答案
1. As explained in the paragraph you quoted, this is because of the phenomenon called "Doppler red shift".
When an object emitting light wave is receding, because the direction of motion of the object is in opposite direction to that of the propagation of light waves, a wavefront emitted by the object will be at a longer distance from the preceding wavefront than if the object is not moving. As such, the distance between two successive wavefronts thus increases, leading to a lengthening of the wavelength.
2. In theory, it is possible. But the speed of the galaxy needs to be very high, reaching 3/4 of the speed of light.
Taking the wavelengths of red and violet light to be 700 nm and 400 nm respectively
using the Doppler shift formula,
change of wavelrngth/original wavelength = speed of galaxt/speed of light
(700-400)/400 = v/c, where v is the receding speed of the galaxy, and c is the speed of light
thus, v = 3c/4 = 2.25 x 10^8 m/s
