Posted on October 26 2018
In classical antiquity, the sacred Seven Luminaries or what we now call the Seven Classical Planets are the seven non-fixed objects in the sky easily visible to the unaided eye: the Moon, Mercury, Venus, the Sun, Mars, Jupiter, and Saturn. Before the age of telescopes, the night sky was thought to consist of two very similar components: fixed stars, which remained motionless in relation to each other, and "wandering stars", which moved relative to the fixed stars over the course of the year. The word planet comes from the Greek word planētēs "wanderer" (short for asteres planetai "wandering stars"), expressing the fact that these objects move across the celestial sphere relative to, what were thought, the fixed stars.
Since then, the influence of this structure of the skies has been huge: for examples the days of the week directly inherited their names from the names of the planets. Similarly, in alchemy, each classical planet was associated with one of the seven metals known to the classical world: silver, mercury, copper, gold, iron, tin and led. Traditionally, each of the seven planets in the solar system as known to the ancients was associated with, held dominion over, and ruled a certain metal.
Astronomical discoveries over the centuries have moved the number of planets in our solar system to eight: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Discovered in 1930, Pluto was reduced to a “dwarf planet” by the International Astronomical Union in 2006 after a highly controversial decision. Nevertheless, more changes to this number may occur in the near future: astronomers are now hunting for another planet in our solar system, a true ninth planet, after evidence of its existence was unveiled on Jan. 20, 2016. The so-called "Planet Nine," as scientists are calling it, is about 10 times the mass of Earth and 5,000 times the mass of Pluto.