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I'm fascinated by the capability of the astronomical data available in V13. (Running 13.0.0.0 on a Mac M1.). Certain data such as altitude and azimuth for a star position should be time dependent but I can't figure out how to specify the time in the EntityValue request.

If I ask for the property with no time object qualifier I think I get a current value:

star = ctrl=Kolchab (* note, I'm not sure how to indicated free form input in this question *)
EntityValue[star, "Azimuth"]
(* Quantity[MixedMagnitude[{347, 5, 5.*10^1}], 
 MixedUnit[{"AngularDegrees", "Arcminutes", "Arcseconds"}]] *)

and if I wait a few minutes and try again, I get a different value:

EntityValue[star, "Azimuth"]
(* Quantity[MixedMagnitude[{347, 32, 3.*10^1}], 
 MixedUnit[{"AngularDegrees", "Arcminutes", "Arcseconds"}]] *)

So, I'm guessing that the data is the value current at the time of the request.

However, I would like to be able to specify a specific time (actually a set of times) but while I see how to specify a data qualifier I don't see how to specify the time.

Any thoughts?

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1 Answer 1

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Use EntityProperty with the provided "Date":

date = DateObject[{2014, 4, 9, 22, 0, 0}];

EntityValue[Entity["Star", "Kochab"], 
 EntityProperty["Star", "Altitude", {"Date" -> date}]]

(* Quantity[MixedMagnitude[{53, 58, 8.}], 
 MixedUnit[{"AngularDegrees", "Arcminutes", "Arcseconds"}]] *)

For multiple dates, map over the list of dates:

date1 = DateObject[{2014, 4, 9, 20, 0, 0}];
date2 = DateObject[{2014, 4, 9, 23, 0, 0}];
dateRange = DateRange[date1, date2, "Hour"];

EntityValue[Entity["Star", "Kochab"], 
 EntityProperty["Star",    "Altitude", {"Date" -> #}] & /@ dateRange]
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  • $\begingroup$ Thanks. This is great. I knew DateObject worked but didn't realize it also could be used to specify the time so was looking for a TimeObject construct. Much appreciated. $\endgroup$
    – jmm
    Dec 29, 2021 at 15:13
  • $\begingroup$ Great :-) Since it provides the solution, please consider accepting the answer. $\endgroup$
    – Domen
    Dec 29, 2021 at 15:23
  • $\begingroup$ Done - and thanks again. $\endgroup$
    – jmm
    Dec 30, 2021 at 0:57

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