The animals are a
clock made of planets.

The oldest layer of the zodiac tracks a single object: Jupiter. To the ancient Chinese it was 岁星 Suìxīng, the year-star. Jupiter circles the Sun once every 11.86 years, and astronomers divided the band of sky it travels through into twelve stations, 十二次. Each year Jupiter steps into the next station. Twelve stations, twelve steps, twelve animals.

The fit is close but not perfect, and the ancient astronomers knew it. A true Jupiter year is 11.86 years, not a clean 12, so the planet gains a full extra station roughly every 86 years. Chinese records corrected for this drift with a leap station called 超辰. That is not the behavior of a superstition. That is people checking their model against the sky and patching the error.

Orbital period: NASA Jupiter Fact Sheet (sidereal period 4,332.6 days).

Before telescopes, exactly five planets were visible to the naked eye. Chinese astronomers named each one for an element, and those names are still the words used today. The Five Elements (五行) you meet in a reading are, at the root, the five wandering lights people actually watched.

Orbital periods: NASA Planetary Fact Sheets. The element-to-planet mapping is the standard classical Chinese naming.

The Chinese calendar answers to two clocks at once. Months follow the Moon: one full cycle of phases, a synodic month, takes 29.53 days. Years follow the Sun: one tropical year is 365.24 days. Twelve lunar months fall about eleven days short of a solar year, so the calendar inserts a thirteenth, a leap month, to stay locked to the seasons.

The rule that makes it work is the same one the Greeks called the Metonic cycle: 19 solar years run almost exactly 235 lunar months, off by only about two hours. That near-perfect coincidence is why Lunar New Year drifts within a window year to year but never wanders off the calendar entirely.

Solar terms are defined by the Sun's apparent ecliptic longitude in 15° steps.

Stack ten Heavenly Stems (天干) against twelve Earthly Branches (地支) and they realign every 60 years, the great cycle that governs your full sign, like Yang Wood Dragon. Sixty is simply the least common multiple of ten and twelve.

But there is a striking coincidence in the sky at the same number. Five Jupiter orbits run 59.3 years. Two Saturn orbits run 58.9 years. Three Jupiter–Saturn great conjunctions run 59.6 years. The two slowest naked-eye planets very nearly reset their dance every six decades, right where the stem-branch calendar resets too.

Jupiter–Saturn synodic period ≈ 19.86 yr; Saturn period ≈ 29.46 yr (NASA). The 60-year alignment is a near-resonance, not exact.