Why do horoscope signs have dates associated with them?

Horoscope signs, also known as sun signs, are given dates based on the movement of the sun through sets of constellations. The sun spends roughly one month in each constellation.

Astrology uses the position of the sun in the sky to calculate and predict events. For horoscopes, this is done using the position of stars and planets currently resting in a particular sign. Astrology has a basis in astronomy, but also uses divination to make predictions, causing scientists to list it as a pseudoscience. The process of the sun moving through the constellations that became the zodiac signs was first observed as early as 1950 B.C., during the first Mesopotamian dynasty.