Do Celestial Time Calculations 

Plot the equation of time—the difference between the Sun's right ascension at noon and the sidereal time at noon.

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X sunpos = SunPosition[GeoPosition[{0, 0}], DateRange[DateObject[{2014, 1, 1, 12, 0}, TimeZone -> 0], DateObject[{2014, 12, 31, 12, 0}, TimeZone -> 0], 10], CelestialSystem -> "Equatorial"]; stime = SiderealTime[GeoPosition[{0, 0}], DateRange[DateObject[{2014, 1, 1, 12, 0}, TimeZone -> 0], DateObject[{2014, 12, 31, 12, 0}, TimeZone -> 0], 10]]; equationoftime = TimeSeriesThread[ With[{diff = First[#][[1]] - Last[#]}, UnitConvert[ Mod[diff, Quantity[24, "HoursOfRightAscension"], Quantity[-12, "HoursOfRightAscension"]], "MinutesOfRightAscension"]] &, {sunpos, stime}]; DateListPlot[equationoftime, PlotLabel -> "Equation of Time", Axes -> True]

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