Google the word ephemeris. Also bear in mind the physical shift of a whole "sign" https://www.youtube.com/watch?v=oQPFoDkGFrU"]Bill Nye on Astrology - YouTube
Signs and constellations aren't the same thing. Constellations are groupings of stars. Signs are 30 degree divisions of the ecliptic. The signs and constellations never exactly lined up because constellations can be more or less than 30 degrees, and often overlap. Signs are basically just a way to evenly divide the ecliptic.