Editing Julian day (section)

==Julian date calculation==
As stated above, the Julian date (JD) of any instant is the Julian day number for the preceding noon in Universal Time plus the fraction of the day since that instant. Ordinarily calculating the fractional portion of the JD is straightforward; the number of seconds that have elapsed in the day divided by the number of seconds in a day, 86,400. But if the UTC timescale is being used, a day containing a positive [[leap second]] contains 86,401&nbsp;seconds (or in the unlikely event of a negative leap second, 86,399&nbsp;seconds). One authoritative source, the [[SOFA (astronomy)|Standards of Fundamental Astronomy]] (SOFA), deals with this issue by treating days containing a leap second as having a different length (86,401 or 86,399&nbsp;seconds, as required). SOFA refers to the result of such a calculation as "quasi-JD".<ref>"SOFA Time Scale and Calendar Tools" 2016, p. 20</ref>