Counting the days

Counting the days Scaliger defined something he called the Julian Period of 7980 years, which was a product of three different dating cycles: The 19-year Meton cycle used in lunar-solar calendars, such as the Jewish one, the 28-year solar cycle, which is the number of years it takes for days of the week to repeat in the Julian calendar and the 15-year indiction cycle used for dating medieval manuscripts. Working backwards 4731 BCE is the last time that all three cycles were in their respective first years.

Mars Athmosphere Loss

Ethan Siegel: NASA’s MAVEN discovers how Mars lost its atmosphere: at some point less than a billion years after Mars formed, its global magnetic field ceased to be, removing the planet’s main source of protection from the solar wind. the atmospheric loss was gradual, and took tens to hundreds of millions of years