Audio Guide：

In 1842, Austrian physicist Christian Doppler found that the relative speed between the sound source and the observer will cause the wavelength and frequency of the sound received to change. French physicist Armand Hippolyte applied this principle to the measurement of celestial objects in 1848. When a celestial object moves closer to the Earth, the spectral lines observed will move towards the blue end. Conversely, when an astronomical object moves away from the Earth, the spectral lines shift to the red end. The phenomena of “blueshift” and “redshift” are a result of the Doppler Effect.