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I'm trying to solve this task:

At what local time is the point of autumn equinox at its upper culmination three weeks after the vernal equinox?

I think it has something to do with the sidereal day (23 hours 56 minutes and 4 seconds), but at what time should I start counting?

Could someone please explain this? Thanks for any help.

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    $\begingroup$ Great question. It requires understanding where the autumnal equinox is located in the sky, what upper culmination means, when the vernal equinox occurs, the significance of the vernal equinox, and the length of the sidereal day. You understand the sidereal day. Do you need clarification on the other items? Or just an explanation of how to determine the answer? $\endgroup$
    – JohnHoltz
    Jul 23 at 17:31
  • $\begingroup$ It would be really helpful if you could provide an explanation and also a clarification on other items. $\endgroup$
    – ALiCe P.
    Jul 24 at 3:16
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On the day of vernal equinox the point of vernal equinox together with the Sun culminates at exactly 12:00 o'clock by local time. The point of autumnal equinox is located at the opposite side of point of vernal equinox on celestial sphere, which means that on the day of vernal equinox it will culminate at 23:58:02 by local time. (24:00:00 less half of 3 minutes 56 seconds.) With each day the culmination will happen 3 minutes and 56 seconds earlier. After 3 weeks the culmination will happen 82 minutes and 36 seconds earlier, or at 22 hours 35 minutes and 26 seconds by local time.

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