Now Try This!

 

The nearest bright star beyond our sun is called Alpha Centauri. It is easily visible in the night sky if you live on Earth’s southern hemisphere. Alpha Centauri is orbited by a planet, the nearest one beyond our solar system.

 

Alpha Centauri is 4.37 light years away. That doesn’t sound too far until you remember that one light year = the distance light travels in a year which is about 10 trillion kilometers! So, Alpha Centauri is about 44 trillion kilometers away (give or take a few billion). How long would it take to travel to Alpha Centauri flying in the Space Shuttle going 28,000 kilometers per hour?

​Left: Alpha Centauri: The nearest bright star beyond our sun at 4.37 light years away. Photo from ESO/Digitized Sky Survey 2.

 

 

Remember v = d/t? Rearrange that equation to find t:

 

time =distance——————velocity t =  d—v 

The distance of 44 trillion kilometers is too big to write out so we use scientific notation. As the Appendix shows a trillion is 10¹² so

 

44 trillion km = 44 x 10¹² km

 

but remember in scientific notation there is only one digit before the decimal so the distance, d, is 4.4 x 10¹³ km

 

And converting the velocity of 28,000 km/hr to scientific notation requires putting a decimal point after the 2 and counting over 4 spaces to the rightmost digit.

 

28,000 km/hr = 2.8 x 10⁴ km/hr

 

Now we are ready to do the problem!

 

t = 4.4 x 10¹³ km/2.8 x 10⁴ km/hr = 1.6 x 10⁹ hr

 

and since there are 24 hrs/day x 365 days/yr = 8,760 = 8.76 x 10³ hrs in a year,

 

1.6 x 10⁹ hr / 8.76 x 10³ hr/yr  = 1.8 x 10⁵ = 180,000 years to reach the star!

 

Clearly, a faster vehicle is required if humans are ever going to travel to the stars!