1 light year = metres. This is equivalent to miles. speed of light is typically given as 3.0*10^8 meters per second, or 186,000 miles per second, so by doing the math yourself the answer can be regenerated any time you need it. so see (186000miles per second)*(60seconds per minute)*(60minutes per hour)*(24hours per day)*(365.25 days per year) gives 5.8697 E +12 miles, very close to the above, but now you know how they got there and need not arbitrarily blindly remember 1 number, and you can PROVE why you believe it. this above method is called dimensional analysis where as in above,