365 days   24 hours   60 mins   60 secs               secs
  -------- * -------- * ------- * -------- = 31,536,000-----
   1 year     1 day     1 hour    1 minute              year  

(Note the cancellation of units)
      
31,536,000 seconds in 365 days 

31,622,400 seconds in 366 days (a leap year) 

31,556,926.08 seconds in a solar year 

and different in a siderial year,  

and lunar year, etc...