It takes light approximately 100,000 years to travel across the diameter of the Milky Way galaxy.

Here's why:

* Milky Way's Size: The Milky Way is a massive spiral galaxy with an estimated diameter of about 100,000 light-years.

* Speed of Light: Light travels at a constant speed of approximately 299,792,458 meters per second (186,282 miles per second).

* Calculation: Since a light-year is the distance light travels in one year, it takes 100,000 years for light to traverse the diameter of the Milky Way.