measuring its red shift. the gravity it exerts. contrasting it against nearby stars. observing its motion across the sky.
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: The speed and general direction of motion of a galaxy relative to the Earth can be determined by
Possibilities:
- measuring its red shift.
- the gravity it exerts.
- contrasting it against nearby stars.
- observing its motion across the sky.

measuring its red shift.