What does the term "red-shift" refer to in astronomy?

The term "red-shift" in astronomy specifically refers to the phenomenon where light from distant galaxies shows an increase in wavelength, causing it to shift toward the red end of the spectrum. This effect occurs due to the Doppler effect, where objects moving away from the observer cause the wavelengths of light to stretch out, or increase.

When astronomers observe the light spectrum from a galaxy and notice that the spectral lines are shifted to longer wavelengths, they can conclude that the galaxy is receding from us. This observation supports the theory of an expanding universe, as it is commonly observed that more distant galaxies exhibit greater red-shifts, indicating they are moving away faster.

The concept of red-shift is crucial in understanding the dynamics of the universe, particularly in relation to the Big Bang theory and the expansion of space itself.