Your birth chart is based upon a snapshot of the sky at your exact time of birth; it is essentially your celestial fingerprint.
It is easy to get confused when trying to understand your Natal Chart and astrology, especially if your zodiac sign changes.
A Natal Chart is a hyper-personalized horoscope which is generated using your birth date, time, place, combined with NASA technology, to create an exact imprint of your sky.
To accurately record this information, it requires an unaltered, standardized time measurement - namely GMT (Greenwich Meridian Time), which is the oldest measurement for time, which is still the foundation of Natal Chart and scientific astrology.
All renowned and practicing astrologists, and all scientifically coded astrology programs and apps, use GMT as the base foundation for accurately determining a Natal Chart.
Confusion comes when there is a large time difference with your current time vs. the GMT, especially for those born on the cusp of a horoscope.
For example, if you were born in California, USA, on the 20th of January at 07:00 am PST - logically, you would assume that you are born an Aquarius. According to accurate astrological predictions of your Natal Chart using GMT time, you were born a Capricorn. This is because the PST time is actually 8 hours behind GMT (so GMT - 8 hours); therefore, you were effectively born on the 19th of January at 11:00 pm GMT, causing the change of your star sign. This is why people born away from the GMT line, on the cusp of a star sign, hold alarming similarities to their neighboring star sign.
So your planetary alignment and the secrets it holds have been cast in time; however, not always in your current timezone.