# Is there a way to get AbsoluteTime to correctly report absolute time differences?

AbsoluteTime supposedly reports the "total number of seconds" between two dates, but it does not. For example, because of the leap second applied at 2012-06-30T23:59:60Z,

AbsoluteTime[{2012, 7, 1}] - AbsoluteTime[{2012, 6, 29}]


should be 172,801, but it returns 172,800. In fact, Mathematica seems to ignore leap seconds altogether:

DateList[{2012, 6, 30, 23, 59, 60.5}, TimeZone -> 0]


produces {2012, 7, 1, 5, 0, 0.5} when it should produce {2012, 6, 30, 23, 59, 60.5}.

Am I missing something here? How are calculations and functions, such as AstronomicalData, that depend on accurate time specifications supposed to work?

Update: This remains the case in version 9.0 and 10.0.2.

Update: Without ever directly acknowledging this as a bug, Wolfram has now notified me that this "issue has been resolved" in 12.1 — 8 years later (though in fact it appears not to have actually been fixed).

• Note that I'd be happy (well, a bit unhappy actually) with an answer that simply clarified Mathematica's concept of a "time". For example, it seems that by "time", it really means "calendar date including hours, minutes, and seconds", so that AbsoluteTime is a bit of a misnomer: it's really "DifferenceBetweenCalendarDatesConvertedToSeconds". – orome Nov 22 '12 at 18:30
• This is known to be a deficiency for a lot of years. I think it will not be changed. – Rolf Mertig Nov 22 '12 at 20:08
• @RolfMertig: So it's easy enough then (I think) to see one implication of this for AstronomicalData: leap seconds are ignored and time is just ticking away according to a uniform clock, but not UTC, so that the data reported by AstronomicalData for a given (*Mathematica) "date" will actually be the data for a different UTC date (what the world outside *Mathematica *means by "date") some seconds away. But that leaves the question: which date? – orome Nov 22 '12 at 20:53
• @RolfMertig, got a Uncompress::corrupt error on your hashed email. Can you fix? – alancalvitti Dec 11 '14 at 17:40
• @alancalvitti: I've tried. They got defensive and angry. Very unpleasant experience. – orome Dec 11 '14 at 17:49

• The question is how to get AstronomicalData to report the "total number of seconds" between two dates, as claimed; not how to calculate them on one's own. – orome Dec 11 '14 at 16:48
• How to interpret the several gaps between regular intervals? years in tai-utc (year only, ignoring month) Import["http://maia.usno.navy.mil/ser7/tai-utc.dat"][[All, 1]] // NumberLinePlot – alancalvitti Dec 11 '14 at 18:05
• Markus Roellig provides a Mathematica routine for $\Delta T$ here. – J. M.'s discontentment Aug 2 '16 at 8:24