Image source: http://library.thinkquest.org/C005462/media/scrossALPHA.jpg
A light year is the distance that light travels in one year, which is 9.46
x 1012 km. The number of light years between the sun and the nearest
star system, Alpha Centauri, is 4.36 light years. This number is determined
by dividing the actual distance by the length of a light year, (4.12 x 1013
km)/(9.46 x 1012 km). When determining this value, the dividing powers
property can be used by subtracting the exponents, which results in 4.12/9.46
x 101 = 0.436 x 101 = 4.36 light years.