$A$ star emits light of $5500 \ \mathring{A}$ wavelength. If it appears blue to an observer on the Earth,it means:

$A$ 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 ....... $\mathring{A}$.

If the shift of wavelength of light emitted by a star is towards the violet end of the spectrum,then this shows that the star is

With what speed should a galaxy move outward with respect to Earth so that the sodium-$D$ line at wavelength $5890 \ \mathring{A}$ is observed at $5896 \ \mathring{A}$? (in $\text{km/s}$)

The wavelength of light coming from a star is observed to increase by $0.4\%$. What is the velocity of the star?

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