Washington: 86,400 seconds, this is the duration a day. But on June 30 because of an extra or 'leap' second the day will officially a bit longer than the usual. NASA has explained the reason behind it. According to Daniel MacMillan, NASA's Goddard Space Flight Center in Greenbelt, Maryland said the Earth's rotation time is gradually slowing down, in account of that leap second is introduced. This is the case according to the time standard that people use in their daily lives - Coordinated Universal Time or UTC. UTC : UTC is the "atomic time" , the time duration duration of one second is based on extremely predictable electromagnetic transitions in atoms of cesium Based on the datat that how long it takes earth to raotate , the average length of the day that is mean solar day is about 86,400.002 seconds long. Typically, a leap second is inserted either on June 30 or December 31. Normally, the clock would ...