People are stupid.
Nothing "changed" from two days ago to today. This is simply some astrologers finally accounting for the fact that the ancient zodiac signs are a few thousand years out of sync with where the sun actually is on a given date.
Not that I believe in any made-up astrology crap anyway, but to say that anything changed so suddenly is just stupid.
I had a star chart program on my computer many years ago and I remember looking up the exact date and time I was born. On that day (July 8th), the Sun was right in the middle of the constellation of Gemini. Despite that, horoscopes all claimed that I was a Cancer. Now finally they've gotten with the times and said that oh, I guess I am a Gemini after all.
If your astrological sign is based on the location of the Sun on the day you were born, then these new dates are accurate for nearly everyone alive today. It's possible that a tiny amount of precession occurred and might push a few really old people with birthdays near the edges of one sign into a different one, but it's a slow process that takes centuries to have a significant effect.
Nothing is different now except in the minds of astrology fans.