How does the red-shift differ from blue-shift?

Red-shift occurs when light moves away, stretching wavelengths; blue-shift happens when light approaches, compressing wavelengths.

Red-shift and blue-shift are phenomena related to the Doppler effect, which describes changes in the frequency of waves relative to an observer. When an object emitting light moves away from us, the light waves stretch out, increasing their wavelength. This shift towards the longer wavelength end of the spectrum is called red-shift because red light has the longest wavelength in the visible spectrum. Red-shift is commonly observed in distant galaxies, indicating that the universe is expanding.

On the other hand, blue-shift occurs when an object emitting light moves towards us. In this case, the light waves are compressed, decreasing their wavelength. This shift towards the shorter wavelength end of the spectrum is called blue-shift because blue light has one of the shortest wavelengths in the visible spectrum. Blue-shift is less commonly observed but can be seen in objects like stars moving closer to Earth.

Both red-shift and blue-shift are crucial in astrophysics for understanding the movement and behaviour of celestial objects. By analysing the light from stars and galaxies, scientists can determine whether these objects are moving towards or away from us. This information helps us learn about the dynamics of the universe, such as the rate of its expansion and the motion of stars within galaxies.

In summary, red-shift and blue-shift are essential tools for astronomers to map the universe's structure and understand its evolution. They provide insights into the movement of celestial bodies and the overall behaviour of the cosmos.