As far as I uinderstand, continuing my research, is that at present (actually, based on observations of 1930, 85 years ago) the exact subdivision of the zodiac according to the classic constellations is in 13 parts of unequal width.
This as described by the vector (arrow) leaving the earth thru the sun and outward bound.
Of course, this is strictly related to Sidereal astrology and has nothign to do, as Steve has explained, with classical tropica astrology whose subdivision is just conventional.
The modern constellation boundaries weren’t defined until 1930 by the International Astronomical Union. With the current boundaries, there are actually thirteen constellations that lie along the sun’s path. The extra one not listed in any horoscope is Ophiucus, the Serpent Bearer, who sits between Sagittarius and Scorpius. Whereas the signs remain fixed relative to the solstices and equinoxes, the solstices and equinoxes drift westward relative to the constellations or backdrop stars.
