What caused the change of the zodiac signs?

Answer 1

The apparent change in the position of the zodiac signs is caused by a natural phenomenon known as precession.

Every 26,000 years, the Earth's axis traces out an apparent set of circles across the sky (one in each hemisphere). Because of this long-term motion, the pole star appears to shift: currently, the star closest to celestial north is Polaris (in the constellation Ursa Minor), but in the distant past it has been Vega, and in another 1,000 years it will be a star called Gamma Cephei.

This same phenomenon is what has caused the apparent shift in the zodiac. Around 2,000 BCE, ancient astronomers (who were also astrologers; at the time there was no difference) noted that on the vernal equinox -- the first day of spring -- the rising sun appeared in a part of the sky we have since chosen to call Aries.

Now it's 4,000 years later, and the Earth has progressed about 2/13th (15%) of the way around its grand precession; or about 1° every 72 years. This is more than enough time for the background constellations to have appeared to have shifted by one full constellation; so now on the vernal equinox, the sun appears to be in Pisces instead... as it has since around the year 100 BCE.

So this 'revelation' is about 2,100 years overdue. In fact, the vernal equinox has already progressed most of the way through Pisces, and is expected to move into Aquarius around the year 2700. Which means that all those new-age followers who've been claiming we're already living in the 'age of Aquarius' have jumped the gun by a bit: 650 years, give or take.

If you want more information on this completely natural phenomenon, please see the attached links.