Why do we have leap years?

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  • Answers.USA.gov. "Standards: Official Time." (Jan. 31, 2012) http://answers.usa.gov/system/selfservice.controller?CONFIGURATION=1000&PARTITION_ID=1&CMD=VIEW_ARTICLE&USERTYPE=1&LANGUAGE=en&COUNTRY=US&ARTICLE_ID=9704
  • Doggett, L.E. "Calendars." Explanatory Supplement to the Astronomical Almanac. 2005. Sausalito, Calif. University Science Books. (Feb. 2, 2012) http://astro.nmsu.edu/~lhuber/leaphist.html
  • Encyclopaedia Britannica. "Sosigenes of Alexandria." Encyclopaedia Britannica Online. (Feb. 2, 2012). http://www.britannica.com/EBchecked/topic/555018/Sosigenes-of-Alexandria
  • The Honor Society of Leap Year Day Babies. "The Honor Society of Leap Year Day Babies." (Feb. 2, 2012) http://leapyearday.com/feb29/home
  • The National Institute of Standards and Technology. "What leap seconds are, how they are implemented and their future." NIST.gov. Jan. 18, 2011. (Jan. 31, 2012) http://www.nist.gov/pml/div688/leapseconds.cfm
  • ROG Learning Team. "Leap Years and Leap Seconds." Royal Museum Greenwich. Dec. 30, 2002. (Jan. 31, 2012) http://www.rmg.co.uk/explore/astronomy-and-time/time-facts/leap-years
  • U.S. Navy. "Leap Years." Naval Oceanography Portal. (Feb. 2, 2012) http://www.usno.navy.mil/USNO/astronomical-applications/astronomical-information-center/leap-year

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