How long would it take us to travel to Alpha Centauri?

On Fri, 4 Jun 1999 you wrote:

> If light travels at 186,000 miles per hour and a star is 75,000 light years
> away how long would it take for the light from the star to reach us. And how
> long would it take for a flight to it. Also could you provide formula to your
> solution.

Hi Bill,

I'll give you some hints to your problem, but I won't solve your exact
problem. I hope that's okay. By the way, light travels at 186,000 miles
per SECOND, not per hour.

First of all, a light-year is the distance light travels in one year. The
star Alpha Centauri is about 4 light-years away, so light from Alpha
Centauri takes 4 years to get to the Earth.

Now, if we wanted to travel to Alpha Centauri, we would have to know how
fast our spaceship is travelling. The fastest rockets move at about
20,000 mph. Suppose we launch one at 20,000 miles per hour toward Alpha
Centauri. How long would it take to get there?

Well, distance travelled equals speed times time, so the time it takes to
travel a distance is that distance divided by the speed, or
4 light-years
-------------
20,000 miles / hour
Now this isn't terribly illuminating. We need to convert units so that we
can do the division. There are 6 trillion miles in a light-year
(approximately), so the distance we need to go is 6 trillion miles /
light-year times 4 light-years, or 24 trillion miles. So, the time it
takes to go to Alpha Centauri is:
12
24 x 10 miles
---------------
4
2 x 10 miles per hour

Doing the division, this trip would take 1.2 billion hours. There are 24
hours a day and 365.25 days per year, so this time in years is 137
thousand years.

That's a long time! Now you can start to see while it is virtually
impossible to visit other stars - even the closest star would take
hundreds of thousands of years to reach!

Thanks for writing,
Kurtis Williams

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