"The Milky Way is approximately 100,000 light-years in diameter."
Well that's quite quick to say, but exactly how far is 100,000 light-years?
A beam of light travels at 299,792,458 metres per second which is 299,792.458 kilometres per second or 186,282 miles per second
If you multiply 186,282 miles per second by the number of seconds in a year you have the number of miles light travels in one year
So 186,282 x 60 seconds in a minute x 60 minutes in an hour x 24 hours in a day x 365.25 days in a year = 5,878,612,843,200 miles
If you travel that far for 100,000 years you travel 5,878,612,843,200 x 100,000 miles = 587,861,284,320,000,000 miles which in words is:
FIVE HUNDRED AND EIGHTY-SEVEN THOUSAND, EIGHT HUNDRED AND SIXTY-ONE TRILLION, TWO HUNDRED AND EIGHTY-FOUR BILLION, THREE HUNDRED AND TWENTY MILLION MILES. APPROXIMATELY.