Nov o1 ( question posted today)
The astronomer observes the same wavelength (from hydrogen) becoming longer when viewed from a source in outer space -red shift.
This is a term used to refer to the wavelength of light becoming longer when they are viewed from a source from the space. If all wavelength of light become longer (just by a little) the visible light would have shifted to the red end of of spectrum (red is longer ) .
There is a red shift due to the source moving away from the observer . Doppler shift is more realistic as we have experience how an ambulance may sound different when it is approaching you and racing away from you . When it moves away the frequency is lower and wavelength will be longer and vice versa. So do expect a blue shift if the source is moving towards the observer, but due to expansion of the universe , red shift is commonly seen from distant galaxies.
