I\'m confused by the many contradictory descriptions I see about how UTC leap se

Question

I'm confused by the many contradictory descriptions I see about how UTC leap seconds are accounted for. I understand that there are various ways to handle them in common practice, and I've seen a variety of formal definitions. But it seems that in scientific practice, they are simply omitted: there is no UTC Julian Day (that is no JD(UTC) value) corresponding to any times during a leap second, and things like ephemeris are generally not reported for leap seconds. There are, of course, events that take place during leap seconds, but if one wants to refer to the time at which they occur, one uses a different timekeeping system (e.g. UT1 or TT).

Is that right? It makes perfect sense as a way to accommodate the ambiguities that leap seconds introduce, and it in fact corresponds to the way some systems (e.g. POSIX) implement them; but it doesn't quite match the definitions I've seen.

Explanation / Answer

As you know, astronomers don't use UT for calculations but Julian Days (JDs). After the calculation is done, resulting JD is converted back to UT, UTC or wanted time zone for public outreach.

Leap seconds can be taken from historical data (e.g. NASA eclipse.gsfc.nasa.gov/SEhelp/deltat2004.html or US Navy maia.usno.navy.mil/ser7/deltat.data) or if those are not available they can be calculated eclipse.gsfc.nasa.gov/SEhelp/deltatpoly2004.html. They are signified as ?T.

?T is then added to JD and that time is called JDE (Julian Ephemeris Day). Or to put it in another way JD is calculated from UT, but JDE is calculated from Dynamical Time (TD = UT + ?T).

Since early 1990's, some publications like Minor Planet Circulars minorplanetcenter.net/iau/services/MPCServices.html) renamed JDE to JDT, where T signifies relation to Terrestrial Dynamical Time.

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