The diameter of the Milky Way disc is approximately 9x10^20 meters. How long does it take light, traveling at 10^16 m/year to travel across the diameter of the Milky Way? Any help with this question would be appreciated. Solution 9*10^20/10^16 9*10^(20-16) 9*10^4 90,000 YEARS TRAVEL TIME ACROSS THE MILKY WAY DISC..