Monday, January 02, 2006
You might have missed this
A leap second is a second added to Coordinated Universal Time (UTC) to make it agree with astronomical time to within 0.9 second.
The first leap second was added on June 30, 1972, and they occur at a rate of slightly less than one per year, on average.
Although it is possible to have a negative leap second (a second removed from UTC), so far, all leap seconds have been. Based on what we know about the earth’s rotation, it is unlikely that we will ever have a negative leap second.
Why do we need leap seconds?
Leap seconds are needed so that users of the astronomical time scale (UT1) can use UTC and know that the difference between the two time scales is never greater than 0.9 seconds. Currently the difference between UT1 and UTC is changing at a rate of about 2 to 3 milliseconds per day, which makes a leap second necessary at an average interval of slightly more than 1 year. Historically, leap seconds have only been implemented on June 30th or December 31st
