MSGID: 1:153/757.0 c91cdaa4   
   TZUTC: -0800   
   CHRS: LATIN-1 2   
                           Astronomy Picture of the Day   
      
       Discover the cosmos! Each day a different image or photograph of our   
         fascinating universe is featured, along with a brief explanation   
                       written by a professional astronomer.   
      
                                 2024 February 29   
      
                            Julius Caesar and Leap Days   
        Image Credit & License: Classical Numismatic Group, Inc., Wikimedia   
      
      Explanation: In 46 BC Julius Caesar reformed the calendar system. Based   
      on advice by astronomer Sosigenes of Alexandria, the Julian calendar   
      included one leap day every four years to account for the fact that an   
      Earth year is slightly more than 365 days long. In modern terms, the   
      time it takes for the planet to orbit the Sun once is 365.24219 mean   
      solar days. So if calendar years contained exactly 365 days they would   
      drift from the Earth's year by about 1 day every 4 years and eventually   
      July (named for Julius Caesar himself) would occur during the northern   
      hemisphere winter. By adopting a leap year with an extra day every four   
      years, the Julian calendar year would drift much less. In 1582 Pope   
      Gregory XIII provided the further fine-tuning that leap days should not   
      occur in years ending in 00, unless divisible by 400. This Gregorian   
      Calendar system is the one in wide use today. Of course, tidal friction   
      in the Earth-Moon system slows Earth's rotation and gradually lengthens   
      the day by about 1.4 milliseconds per century. That means that leap   
      days like today will not be necessary, about 4 million years from now.   
      This Roman silver coin, a denarius, depicts Julius Caesar (left) and   
      Venus, Roman goddess of love.   
      
                        Tomorrow's picture: pixels in space   
        __________________________________________________________________   
      
          Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)   
               NASA Official: Amber Straughn Specific rights apply.   
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                         A service of: ASD at NASA / GSFC,   
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                                & Michigan Tech. U.   
      
   --- BBBS/Li6 v4.10 Toy-6   
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