Question

An astronomer looks at the Andromeda galaxy (the other large galaxy in the Local Group) through her telescope. How long ago did that light leave Andromeda?

Answer 1

`2.537* 10^(6)\ years`

Step-by-step explanation:

Distance to Andromeda galaxy

`2.537* 10^(6)\ ly=2.537* 10^(6)* c* y`

Speed of light is

`c=3* 10^8`

Time is given by

`t=(Distance)/(Speed)\\\Rightarrow t=(2.537* 10^(6)* c* y)/(c)\\\Rightarrow t=2.537* 10^(6)\ y`

Hence, the light from Andromeda left
`2.537* 10^(6)\ years` ago