luckily for us, many people are more curious than others...
I'm not talking about satisfying a "curiosity" and the length of time I'm talking about would take far more than a few generations (try a hundred). One precessional "age" lasts about 2100 years and it takes 26000 years for all the zodiacal constellations to cycle through the vernal equinox. Other than the Egyptians, there are no known civilizations that lasted more than what, a thousand years, maybe? And even the ancient Egyptians had all kinds of societal upheavals that wiped out great chunks of their learning. So, absent thousands of years of continuous, recorded, direct observation, or a firm understanding of planetary mechanics (which they supposedly did not have), how did the ancients accomplish what they did?