In Yalta, on February 7 at 10 pm, Regulus (a Leo) was observed. Determine at what altitude and in what azimuth this star was observed at this moment in Yalta?
We write out the latitude of Yalta from the table: f = + 45o, and the coordinates of Regulus (a Leo): a = 10h, b = + 12o.
By calculation, we find the sidereal time of the moment of observation as follows: on February 7 at 0h sidereal time s = 21h. 7th February 10h pm time = 21h + 10h = 31h or 7h.
Then, having drawn the celestial sphere for Yalta, we will immediately determine the position of the vernal equinox point (y) for a given moment in the figure, since the hour angle of the vernal equinox is equal to sidereal time at the given moment, i.e. in this case 7h.
Now, knowing the coordinates of Regulus (a Leo), we first draw a declination circle RP (a = NuER = 10h) in the drawing, and then plot the declination and position M of the star a Leo (b = NRM = + 12o) on this circle.
Drawing a vertical through point M, we get the desired answer: azimuth: A = NSK = 70o east (approx.), Height: h = NKM = 40o (approx.).
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