Why did Mesoamerican priests observe the Sun, Moon, and Venus?

Mesoamerican priests observed the Sun, Moon, and Venus primarily to track the passage of time, manage complex religious calendars, and perform divination. Their astronomical observations were deeply integrated into their religious and social life, serving several key purposes:123

• Timekeeping and Calendars: Priests used the motion of celestial bodies to maintain the Aztec calendar and the Maya calendrical system, which were essential for organizing rituals, ceremonies, and agricultural cycles. These systems tracked the solar year and sacred cycles, such as the 260-day tzolkin or tonalpohualli.4135
• Divination and Fate: Priests, such as the Tonalpouhque among the Aztecs, were trained in calendrical divination. By observing the heavens, they could determine the "favorable or evil influences" attached to specific days, helping people decide when to undertake important enterprises or interpret the significance of a child's birth date.51
• Religious and Mythological Significance: Celestial bodies were considered divinized entities. For example, the Sun was associated with gods like Tonatiuh, and Venus was linked to Quetzalcóatl. Priests tracked these bodies to align public rituals and theatrical dramas of myths with their movements.641
• Scientific Precision: Mesoamerican civilizations achieved remarkable accuracy in calculating the solar year and the synodical revolution of Venus, recording this data in documents like the Dresden Codex to predict events such as solar eclipses.15