Final answer:
The zodiac signs are used to determine an individual's sun sign, but the names of the signs no longer match the constellations they were named after due to the shift in the constellations over time.
Step-by-step explanation:
The zodiac signs are used to determine an individual's sun sign, which represents the zodiac sign the Sun was in at the moment they were born. However, due to precession, the constellations of the zodiac have shifted over time. This means that the astrological signs and the real constellations are now out of step, with the sign of Aries, for example, occupying the constellation of Pisces. When looking up your sun sign, it's important to note the sign before the one that includes your birthday to find the correct constellation.