Question about andromeda?10 points for best answer?

They are saying that andromeda is 2.5 million lightyears away from our galaxy.Then it must have took atleast 2.5 million years for the scientists to find this(if they have used something at the speed of light)Its confusing.How is it possible?Did the scientists started working on this before 2.5 million years ago?Can anyone pls explain me?According to what i heard was we are viewing the andromeda as it was before 2.5 million years ago(cuz light takes atleast 2.5 million years to travel to the andromeda)