At the time Nostradamus lived, astrology was not an occult art. It was considered a science that even several popes learned. It was believed that events in the sky reflected events on Earth, i.e., the Parthenian Magi who came looking for the newborn King of the Jews, because they saw His star rising in the heavens. It was only after Galileo showed how the movements of the planets could be predicted mathematically did it become being used for divination.
Actually, it goes back quite further than that. Easter is supposed to be on the first Sunday after the first full moon of Spring. This means you need to know when spring begins, usually determined by the Spring Equinox, which means making astronomical observations to ensure the correct dates were used. The Vatican Observatory originally was just a platform on top of a tower where you could set up instruments to keep track of the movements of the stars, etc. Aloysus Lilius was the Vatican Astronomer under Pope Gregory XIII. He had been keeping track of the sun by means of a stick set into the platform. Every day for a few years he had been marking where on the platform the shadow of the stick was when the sun was at its highest point (aka, noon) and noting the date. One day in 1581, he invited His Holiness to the Observatory to show him something. Based on the position of the shadow at noon over a period of years, Lilius was able to show the pontiff that the Julian calendar being used was off from the solar calendar by at least 11 days. This led to the promulgation of the Gregorian Calendar in 1582 which was to be used in every Catholic country in the world. The Vatican Observatory was used in astrology, which was considered a science at the time, at least until Galileo showed how the movements of the planets were governed by math. It was also used to develop star charts, which were essential in navigation, as well as scientific studies. The "two and a half centuries" noted above was when light pollution began to be a problem in Rome, and the Vatican Observatory was moved to a new location outside of Rome.
Everything moves in cycles. Astrology is different than Astronomy, but both have a common origin. The Magi were star gazers and recognized the sign of the Messiah in the heavens. There are several types of calendars used in society. Lunar, Solar, Lunar-Solar, Astronomical, and Liturgical. There are phases and cycles in nature, which align coincidentally. Despite entropy, the more disordered the universal system becomes, the more congruent these alignments are. “Everything moves in cycles, every once and awhile Mother Nature let’s us know how small we really are”. -Bhodi (Point Break) (the above quote comes from a discussion about which is the biggest wave ever ridden, for the record it is in Nazare, Portugal. The name is Portuguese for Nazareth. The first church in the old city was built in honor of the Blessed Mother for saving the life of a Templar Knight, who rediscovered a statue brought from the Holy Land, supposedly crafted by St. Joseph and painted by St. Luke.).
