Astronomers have observed that the light coming from distant galaxies appears redder than the light coming from nearer galaxies. This phenomenon is known as redshift. The visible spectrum of light ranges from violet (shortest wavelength) to red (longest wavelength). When an object moves away from us, its light waves get stretched out, causing them to shift towards the red end of the spectrum. This is known as the Doppler effect.
The Doppler effect is a change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. In the case of light waves, if an object emitting light is moving away from us, the wavelength of the light waves will appear longer (shifted towards red), and if it is moving towards us, the wavelength will appear shorter (shifted towards blue).
Astronomers use this phenomenon to study the motion of distant galaxies. By analyzing the spectra of light emitted by these galaxies, they can determine whether they are moving towards or away from us. If a galaxy's spectrum shows a redshift, it means that it is moving away from us. The greater the redshift, the faster it is moving away.
This observation led to the development of the Big Bang theory, which suggests that the universe began as a single point and has been expanding ever since. The redshift observed in distant galaxies provides evidence for this expansion.
In summary, astronomers conclude that distant galaxies are moving away from Earth based on the observation of redshift in their spectra. This indicates that they are receding from us and provides evidence for the expansion of the universe.
Astronomers have observed that the light coming from distance galaxies appears redder than the light coming from nearer galaxies. With the help of the visible spectrum (blue color has the shorter wavelength, and red color has the longest wavelength), explain why astronomers conclude that distant galaxies are moving away from the Earth?
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