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I live in Lehi, Utah, USA and I want to know what time of day it was on sidereal time on February 25th, 2023. Someone said it was 3:32 AM and I wanted to check and see if that was true.

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  • $\begingroup$ Needs detail or clarity (a close reason) $\endgroup$
    – Starship
    Commented Mar 28, 2023 at 17:49
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    $\begingroup$ You may want to add your time zone with it's offset to utc $\endgroup$ Commented Mar 28, 2023 at 17:50
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    $\begingroup$ Lehi is mountain time, UTC -7 so 13:30 is 20:30 UTC $\endgroup$
    – James K
    Commented Mar 28, 2023 at 19:26

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So the local sidereal time is the right ascension of objects on the Meridian at the given time.

Lehi on 25th of February (assuming US style date) is in Mountain time zone, UTC-7, so 13:30 is 20:30 UTC

Using Stellarium, objects on the meridian at that time and location with an azimuth of 180, have a right ascension of 23 hr 24min 23 seconds (accounting for precession) or 23hr 23min 13sec (with J2000.0 coordinates). So this is the local sidereal time of 13:30 Mountain time in Lehi.

Working the other way, a sidereal time of 13:30 occurs at 10:37 UTC or 03:37 Mountain time. There is a slight difference if you use J2000 coordinates, it moves it to 03:38.

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  • $\begingroup$ I think the OP says that the sidereal time is 13:30 and they want to check if that corresponds to 3:32 Mountain Time. $\endgroup$
    – PM 2Ring
    Commented Mar 30, 2023 at 7:41
  • $\begingroup$ You may be right... working backwards... $\endgroup$
    – James K
    Commented Mar 30, 2023 at 16:56
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13:30 local sidereal time means the first point of Aries was 202.5 degrees west of you. With Lehi at about 111.9 W, the GHA of the first point of Aries was about 314.4. Referring to an almanac and interpolating the UTC time was 1033. With Lehi in CST that would be 4:33 AM.

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