In the context of the Doppler effect in light,the term 'red shift' signifies:

$A$ rocket is moving away from the Earth at a speed of $0.2c$,where $c$ is the speed of light. It emits a signal of frequency $4 \times 10^7 \text{ Hz}$. What will be the frequency observed by an observer on the Earth?

If a source of light is moving away from a stationary observer,then the frequency of light wave appears to change because of

$A$ star emitting radiation at a wavelength of $5000 \; \mathring{A}$ is approaching Earth with a velocity of $1.5 \times 10^6 \; m/s$. The change in wavelength of the radiation as received on Earth is ....... $\mathring{A}$.

$A$ star is moving away from the Earth. An observer on the Earth will see the wavelength of light coming from the star as:

$A$ star is moving away from the Earth with a velocity of $100 \ km/s$. If the velocity of light is $3 \times 10^8 \ m/s$,then the shift of its spectral line of wavelength $5700 \ \mathring{A}$ due to the Doppler effect will be ..... $\mathring{A}$.