A Comparison of the Positionof the Sun Over Time
The following images display the position of the sun on 1 January at 500-year intervals. The shift is caused by the precession of the Earth. Simply put, the Earth is wobbling on its axis (just like a spinning top) at a rate of roughly one wobble every 26,000 years. This not only puts the sun in a different position relative to the stars, but the north star is drifting as well. Stargazers of 4000 years ago probably would have called Kochab the north star, at that time it was closer to the North pole than Polaris. Notice that during the time in which the Greeks started using the individual's birth date to determine personality and prediction (c. 250 BCE), and when Ptolemy wrote his works on Astrology, defining Western Astrology for future generation (c. 150 CE), someone born on 1 January would have indeed been a Capricorn. But today he or she would in fact be a Sagittarius.
The perceptive reader will notice that the leap from 1500 CE to 2000 CE is much larger than the rest. That is due to the fact that in the year 1582, when the Gregorian calendar replaced the outdated and incorrect Julian calendar, 10 days were dropped out of the month of October in order to correct the drift in the calendar caused by the fact that the Julian calendar did not include the 400-year leap years. In order to correct the situation, in 1582 the dates from 5 October to 14 October were skipped. Thus, in the Gregorian calendar (the one we use today) the day after 4 October 1582 is actually 15 October 1582.