Modified Julian Date

[genkihenkie]

Is there an easy way to show the time in Modified Julian Date (MJD) in a time bar?

I'm working on a tool for monitoring observations and this is a must that came up for Astronomers.
Maybe someone faced it before?

[jmad]

I found this [1] helpful as a good start. The page shows the various available time scales used in astronomy. This page gives also a simple algorithm for converting UT1 to JD(UT1). The modified JD has a constant Offset from JD of 2400000,5 days. I would start here with calculatons.

UTC differs from UT1 max. 0.9s which allows a good approximation in the conversion of WinCC OA timestamps (which are in UTC).

For astronomical calculations an ephemeridical time scale would be more helpful. Here the terrestrical time (TT) comes into the game and based on this the Julian Daycount JD(TT). TT differs from UT1 by a variable amount of seconds (called Delta-T). Find a good overview here [2] and here [3] with a delta-t table and estimations.

[1] https://en.wikipedia.org/wiki/Julian_day
[2] http://tycho.usno.navy.mil/systime.html
[3] http://stjarnhimlen.se/comp/time.html

[genkihenkie]

Thanks Jörgen, that helps. I love that the more you understand WinCC and it's features, the more confused you get when people ask for more random features.