Seventh Heaven: Decoding the days of the week For almost 2000 years—from the time of Aristotle until the early 17th century—popular theory posited that the earth was the center of the universe, and that everything in space rotated around it in concentric spheres filled with a heavenly fifth element called quintessence. Astronomers believed that the turning of these spheres accounted for the orbits of the heavenly bodies, and that they moved to the music of angels and to the celestial hum of ever-turning planets known as “the harmony of the spheres.” These spheres gave us the days of our week: Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, and Saturday. How? While the theory of the heavenly spheres has been long since debunked, it was considered fact for centuries, so much so that hundreds of generations made all sorts of creative explanations for the lights that appeared in the sky. It wasn’t until 1572 when the Danish astronomer/alchemist Tycho Brahe recorded a new star in the constellation of Cassiopeia that people began to question the theories of celestial immobility. Granted, the Polish astronomer Nicolaus Copernicus had started the revolution toward heliocentricism (the model we accept today in which the earth and other planets orbit the sun) in 1543 with his book On the Revolutions of the Celestial Spheres, but that’s another story for another day. The Renaissance poet John Donne describes the idea of the harmony of the spheres in a work from his collection Divine Poems, titled “Upon the Translation of the Psalms by Sir Philip Sidney and the Countess of Pembroke his Sister.” Make all this All, three choirs, heaven, earth and spheres; The first, heaven, hath a song, but no man hears; The spheres have music, but they have no tongue, Their harmony is rather danced than sung. By “all this All” Donne refers to the known universe, but what does “heaven, earth and spheres” mean? In order to understand what he’s talking about we’re going to have to back up a few millennia. Apart from the stars, ancient Babylonian and Roman astronomers could identify seven major orbs in the sky: the Moon, Mercury, Venus, Mars, Jupiter, Saturn, and of course the Sun (Uranus, Neptune, and Pluto—which in 2006 lost its official “planet” title—were still out of view at this time). These five planets plus the Sun and Moon are what Donne means by “the spheres.” These astronomers believed that each major celestial body was encased in its own ring of crystal, rings dubbed “the seven heavens,” with the earth at the very center. But the “heaven” Donne refers to is the “seventh heaven,” the realm of God and the angels, which floats around the whole system and is filled with stars. It’s a beautiful concept that has appeared in centuries of literature, but the seven spheres did more than give metaphysical poets something to write about: they gave us the seven days of the week. Each sphere correlates with a different day, which using modern Latinate roots, begins with the Moon for Monday and ends with the Sun for Sunday. The Babylonian seven-day calendar was initially based on the monthly lunar cycle, a calendar effective enough to withstand the Roman invasion. The ancient Roman calendar adhered to an eight-day nundinal week that coexisted with the seven-day Babylonian cycle throughout Roman imperialism. In 45 BCE, Julius Caesar instituted the Julian Calendar that followed a seven-day cycle. It was not until Emperor Constantine adopted the Julian cycle officially in 321 AD that the seven-day week was set in stone, and the names of the Roman Gods were given to the planets for which each week day is named. Even though we no longer think of the earth as the center of our universe, the nomenclature derived from this outdated conception of our planetary system still remains. Find the history of these days: Tuesday, Wednesday, Thursday, and Friday.