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I have a latitude / longitude / time of a location on Earth, I need to calculate the Right Ascension / Declination that's overhead at the time provided.

So far I've found out that Right Ascension is the same as the sidereal time for the location but I haven't found any information about declination.

I'm trying to set my overhead viewing location in the web portal of World Wide Telescope. It defaults to "now" but I want to show 10PM and there's no way (that I've found) to set time through the javascript interface. I can however set Right Ascension and Declination, hence my question.

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    $\begingroup$ The declination will be the same as the latitude. ie the point at zenith will have the RA equivalent to the sidereal time and the declination of the the latitude of the observer. $\endgroup$
    – adrianmcmenamin
    Mar 26, 2016 at 23:40
  • $\begingroup$ Awesome, thanks! I'll give it a try on Monday when I get into work $\endgroup$
    – scottinthebooth
    Mar 27, 2016 at 3:11

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The declination of the point overhead (zenith) is the same as the observer's latitude. The RA of the point transiting zenith at any given time is the equivalent of the local sidereal time.

(Alternatively, the local sidereal time is RA of the observer's meridian.)

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