# Find the sidereal clock reading and the altitude at which Arcturus will be in Petersburg (a Bootes, a = 14h12m, b = + 20) at the moment

Find the sidereal clock reading and the altitude at which Arcturus will be in Petersburg (a Bootes, a = 14h12m, b = + 20) at the moment it crosses the eastern part of the first vertical.

The world axis PP1 runs at an angle of 60 ° to SN, and the parallel of KL is + 20 ° from the equator EQ. The intersection of KL with CZ gives us point D. On KL, as on a diameter, draw a circle and a straight line DM1, perpendicular to KL, up to the intersection with this circle MK1L; then РKFM1 = t = 262 = 18h48m and the required hour angle will be. To find the height of the luminary, draw a straight line GH parallel to SN through point D and measure it with a protractor INH or, anyway, PNCH = h = 23o. Knowing the hour angle t and right ascension a, we will also find the sidereal time at this moment, which will be s = t + a = 18h48m + 14h12m = 9h0m. Thus, at the moment Arcturus crosses the eastern part of the first vertical in St. Petersburg, sidereal time will be 9 hours, and the height of Arcturus will be 23о.

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