Getting the Equation of Time value in a script

[101610]

I'm trying to get the equation of time value in a script for further calculations. My goal is to get the value displayed by the Equation of Time plugin but I get slightly different values.

I have tried two approaches so far:

1. EquationOfTime Class: I can enable the plugin and show the value on screen, but it looks like there isn't a public slot to actually get that value in a script. Is that correct, or did I miss something?

2. Calendar Class: I managed to get a value using Calendar.equationOfTime() (see code below) but it differs slightly from what the plugin displays. I haven't tested exhaustively but noticed differences between zero and a couple of seconds (see the screenshot for an example).

The scripting documentation for Calendar.equationOfTime() notes: We use functions from Stellarium instead of the functions from CC:UE 14.20. Therefore, I expected it to give the exact same value as the core plugin.

Is there a better way to get the equation of time value in a script or is this expected behavior?

Note on my implementation below: I calculate RD (Rata Die) as core.getJDay() - 1721424.5 to obtain a double that includes the time of day, rather than Calendar.fixedFromJD() which returns RD as an integer. I am trying to track the value as it changes during the course of a day, just like the plugin does.

// Enable the Equation of Time plugin for comparison
EquationOfTime.enableEquationOfTime(true);
EquationOfTime.setFlagMsFormat (true);

// Output the equation of time value in seconds calculated using Calendar.equationOfTime
var UTC = core.getDate();
var localTime = core.getDate("");
var JD = core.getJDay();
var RD = JD - 1721424.5;
var eqt = Calendar.equationOfTime(RD) * 86400;

core.output ("UTC: " + UTC 
		   	+ "     Local: " + localTime 
			+ "     JD: " + JD.toFixed(5)
			+ "     RD: " + RD.toFixed(5)
			+ "     Equation of Time: " + eqt.toFixed(2) + " s");

26.1 Qt6 on Windows 11

[alex-w]

Hmm... the last member of equation is different in Calendars plugin and in the Core of Stellarium.

@gzotti any comments, please

P.S. Aha, equation of time in Calendars plugin give result in fractions of a day...

[gzotti]

Must check the code in Calendar, obviously... not today, though. The dedicated EoT plugin should also have a public slot for it, though.

[gzotti]

Solution: New scripting function. See #4975

[101610]

Great to see this in 26.2 already.
Thank you!