13/01/2026
Congrats to the Chosen Ones for figuring out the Moon's orbital period 700 years after Hipparchus (c. 129 BC) figured it out, I guess?
It takes the moon one month to orbit the earth.
Well, almost.
According to the Talmud, which was compiled in the fifth century, the moon's orbit is exactly 29.5 days plus 793/1080 parts of an hour, or, in modern parlance, 29.530594 days.
That's an incredible number, which the Talmudic sages derived from various traditions passed down throughout the ages. That number isn't unique to Jewish tradition, although carrying it to the sixth decimal point is an unusual level of accuracy.
Knowledge of the moon's cycle is essential to establishing a Jewish calendar, and, depending on how a month is calculated, determines when the different festivals and holidays take place throughout the year.
Incredibly in 1996, NASA, using satellite observations plugged into celestial mechanics mathematics, calculated the lunar month to be 29.530588 days, which is about only 0.5 seconds off from the number the Jewish people have been working with for centuries.