A question sent in to New Scientist reads,
"My wife told me I should get out more. I replied that I am just about to celebrate my 66th free trip around the sun. Can anyone tell me how far I have traveled around the galaxy during that time?"
All of the information required to answer this question to a ballpark level of accuracy — along with a little elementary arithmetic — can be found in the Galaxy Song from Monty Python's comedy film The Meaning Of Life.
"We're thirty thousand light-years from galactic central point,
We go 'round every two hundred million years..."
So the circumference of the Earth's orbit is (roughly) pi times two times thirty thousand light years. That's approximately 188,495 light years. And we take 200 million years to complete an orbit, which means each year we cover 188,495/200,000,000 light years, which is 0.00094 light years.
So how far is a light-year?
"As fast as it can go, the speed of light, you know,
Twelve million miles a minute, and that's the fastest speed there is"
Twelve million is actually a bit high. C is precisely 299792458 meters per second¹, which is 186,282.4 miles per second, and that works out to 11,176,943 miles per minute. 186,282.4 miles times 86400 seconds per day times 365.24 days per year gives 5,878,464,425,192.5 miles to the light year. Each year we travel 0.00094 of those around the galaxy, which is 5,525,756,559.7 miles, or just over five and a half trillion miles. Multiply by 66 and you get 364,699,932,939 miles, give or take a few hundred yards.
So there's your galactic travel — call it 364.7 trillion miles over 66 years. I'm pretty certain that many frequent flyer miles upgrades you to a first-class seat.
¹ Yes, PRECISELY
299792458 meters per second. Because that's how we now define the meter: 1/299,792,458 of the distance traveled by light in a vacuum in free space in one second.