Stellarium

Proposal for setting and display of time scales, date scales and time zones

Asked by Volker H.

Following a short discussion with Alexander Wolf I propose to add settings and display of date scales, time scales and time zones. Here are my initial ideas:

• All date/time related settings of Stellarium could extend the existing Stellarium date/time dialog window and a button "Settings" could be added.

• Once "Settings" is selected the date/time dialog window gets extended by a number of tick-boxes, time displays etc. which allow

o the setting of the desired date and time value (in the current windows as well as in the extended window).
o the selection of different time scales (UTC, UT1, TAI, TT, TDT, older time scales, etc.).
o the selection of different deltaT algorithms.
o the selection of different date scales (julian, gregorian, proleptic gregorian, etc.).
o the various settings to become the "Stellarium default settings" via a button "set as Stellarium default".
o the various settings to become the "Stellarium start up settings" via a button "set as Stellarium start up". This could include the time settings from "Stellariums configuration dialogs".
o the display of the individual time values next to the applicable time scale tick-boxes.
o the display of the individual date values next to the applicable date scale tick-boxes.
o the display of the related JD, MJD, etc.
o the display of the deltaT value.
o the display of local apparent time, local mean time, equation of time, sidereal time etc.

 • Pending on the entered date the possibility to set of certain time scales could get enabled or disabled. This has to be in accordance with the "official introduction" of certain time scales.

• The collapsed date/time dialog could display the selected date scale behind the date value and the selected time scale behind the time value.

• The current date/time display in Stellariums button menu bar could be extended accordingly and while hovering over it all date/time values could be displayed

• As an alternative to the input of date and time values the extended date/time dialog could also allow JD, MJD, Besselian year etc. as input values.

• Regardless of JD, MJD, Besselian year being the input values the small date/time dialog should always show the related date and the related time.

• If date and time values being the input values the JD, MJD, Besselian year fields should always show the related values.

• All other displayed time scales should be set accordingly

• Selection of a time zone different from the home time zone should be possible in the above context.

Not being an expert myself I hope that the Stellarium experts will understand what I am heading for.

With kind regards
Volker

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gzotti (georg-zotti) said : 		#1

Seeing and being able to set JD/JDE[=JD in ephemeris time]/JulianCalendar/proleptic Gregorian dates (maybe with adjustable calendar switch date?) could be interesting.

Another issue is DeltaT. Please find us a definite, reliable guide to adjust older DeltaT models to be used with VSOP/ELP.

In our context, I don't see a meaningful distinction between ET, TDT, and TT, they are just successors, right? And with a difference below 1s, I don't really see the benefit of displaying all of TAI/UTC/UT1/... Stellarium is first and foremost creating pretty imagery, not text. There may be dedicated software already available for this.

Where would we e.g. get the information on defined leap seconds in the 1980s? How would you fill the TAI field for e.g. 650B.C.? Will the values make sense?

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Volker H. (hvolker) said : 		#2

Hallo Georg,

understanding your point of view I would welcome the implementation of any subset of my proposal.

With respect to the deltaT issue I have mixed emotions. To me it appears to be very much a subject of academic nature. Nevertheless deltaT expressions were implemented in Stellarium and somewhat uncertain deltaT values may be better than no values at all. I may contact the creator of the jParsec library. Maybe he has enough knowledge to give us a reliable guide for the adjustment of older deltaT models to be used with VSOP/ELP..

In my proposal I tried to explain that only meaningful time values should be displayed (e.g. TAI should only be displayed for dates following the introduction of TAI, leap seconds only after their introduction etc.). If this is followed it could help to understand the development and introduction of the different time scales. To not overload Stellarium certain hints could be given rather than to display all values (like UTC and UT1 differ by not more than 1s). You find a lot of time scale related publications and there were obviously good reasons for publishing them.

Please bear in mind that I and maybe many others look at these things with unprofessional eyes trying to learn more about astronomy. Stellarium is a very nice tool to support this attempt. In this context I do not agree with your remark that "Stellarium is first and foremost creating pretty imagery".

Anyway, many thanks for your prompt comments. I look forward to the further development,

With best wishes
Volker

-----Ursprüngliche Nachricht-----
Von: <email address hidden> [mailto:<email address hidden>] Im Auftrag von gzotti
Gesendet: Dienstag, 20. August 2013 14:56
An: <email address hidden>
Betreff: Re: [Question #234317]: Proposal for setting and display of time scales, date scales and time zones

Your question #234317 on Stellarium changed:
https://answers.launchpad.net/stellarium/+question/234317

gzotti posted a new comment:
Seeing and being able to set JD/JDE[=JD in ephemeris time]/JulianCalendar/proleptic Gregorian dates (maybe with adjustable calendar switch date?) could be interesting.

Another issue is DeltaT. Please find us a definite, reliable guide to adjust older DeltaT models to be used with VSOP/ELP.

In our context, I don't see a meaningful distinction between ET, TDT, and TT, they are just successors, right? And with a difference below 1s, I don't really see the benefit of displaying all of TAI/UTC/UT1/...
Stellarium is first and foremost creating pretty imagery, not text.
There may be dedicated software already available for this.

Where would we e.g. get the information on defined leap seconds in the 1980s? How would you fill the TAI field for e.g. 650B.C.? Will the values make sense?

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