For many centuries we have tried to understand our universe. Ancient societies have made star charts, and have been giving names to celestial bodies they observed with their naked eyes. A lot of the stars and constellations we know today have been originally named by a very influential society; the ancient Greeks.
In the oldest Greek literature available, the Iliad and Odyssey, Homer talks about the constellations Orion and Ursa Major, and mentions different star clusters. It is safe to say that the Greeks knew a lot about the stars. In the 6th century BC, philosophers described the universe as our (flat) planet in the center surrounded by rings of fire.
The ancient Greek astronomers have been very influential for our knowledge of the stars and the sky. Many terms we use today derive from ancient Greek. Planets for example, comes from πλανήτης (planētēs), which means something like wanderers. The astronomers noticed objects moving across the skies. They discovered 5 planets with the naked eye and they named them Hermes, Aphrodite, Ares, Zeus and Cronus. It wasn’t until Roman times that these planets changed names and became the planets we know today: Mercury, Venus, Mars, Jupiter, and Saturn.
Plato’s view on the stars and planets
In the 5th century BC, Plato came up with some interesting theories about stars and their trajectory. He said that planets didn’t have one singular, but several circular tracks. Each star and planet has an orbit within an orbit. This, according to Plato, explained the irregular behavior of some of the celestial bodies. He says scientist should study astronomy as an exact mathematical science as their motions were regular and circular, despite their irregular behavior.
In the first century BC, Posidonius attempted to measure the size and the distance of the sun. It would take many centuries before astronomers managed to get it right, but it shows that the interest shown in astronomy was a very important part of Greek science.
The astronomy of Ptolemy
The most important Greek astronomer was Ptolemy. This Greco-Roman scientist wrote a leading book about stars named the Almagest. Based on the already available knowledge from ancient Egyptian astronomy and the research older Greek scientists have done, the Almagest was considered a true piece of art. In one of the chapters, Ptolemy describes the position of more than a thousand stars in their constellations. This can be considered the very first star catalogue.
Even Ptolemy believed that all the planets, the moon, sun, and other stars revolved around the Earth. After careful tracking and star charting he discovered some stars were fixed in the sky. The Almagest also explains the solstices, the motion of the sun, the length of the year. Scientists used this book even 1200 years after it was written, making Ptolemy one of the biggest astronomer in Western history.
The Greeks were not the only Masters of the Stars. Before them, the Egyptians already did extensive research about constellations and star mapping as you can read in this post. In our next episode in the series, we will talk about The Romans and their calendar(s). Lots of aspects of modern day society derive from the Romans, just as our knowledge of the stars.