Before the 15th century, astronomy and astrology were joined, the paran is the same as astronomy, for if a star or planet is rising with the Sun this is visually calculated on the horizon, however Claudius Ptolemy used an inaccurate measure called projected, and many astrologers still use this measure to this day. What he did was tie all the stars to the ecliptic, being the imaginary path of the Sun across the sky, which appears to move approx. one degree per day.
Ecliptic traces the sun’s path | EarthSky.org
Fixed stars move slightly, so can slowly become out of synch with any intended alignment after a few centuries, which is called Axial Precession, link below:-
Axial precession - Wikipedia
Yet what Claudius Ptolemy proposed by tying the fixed stars to the ecliptic means, to be accurate, then all the stars would be in a line following the Sun across the sky. Obviously this doesn't happen, the sky is full of stars, most are no where near the ecliptic, so this method is totally inaccurate!
Almagest - Wikipedia
The above info is directly connected to the last astrology chart i posted, it would seem that the builders of the Gregorian Calendar had switched methods for 1st January 1583 when ten days had been taken out of the calendar in 1582.
On previous picture, the thick line upwards is called the M.C. which is 09 degrees 08 minutes Cancer, by looking at the bottom section of the chart, you will see that Sirius was 08 degrees 21 minutes Cancer, so within one degree, which is the margin for fixed stars that astrologers use with inaccurate projected measure, so Sirius was conjunct the M.C. for two centuries from 1st January 1583 at midnight!