We begin this journey, this Cosmic Quest, with a story about human curiosity and infatuation with the stars. As a species, we began this journey the moment the first human looked at the stars and wondered what they were. It’s only natural to start something called Cosmic Quest with the earliest quests the human kind has undertaken in its search for answers.
It is in our nature to seek answers, to find out more about our surroundings, to learn. Our learning capabilities went hand in hand with survival of our species in the early days and they still do today. By trying to answer questions, we learn how to think, and by learning how to think, we learn how to adapt. This has made us dominant species on our planet, the only species capable of exploring the Universe.
You may think that wolves howl at the Moon, but it turns out it is only a human misconception. To wolves, and all other animals, the Moon, the Sun and the stars are just part of their natural habitat just like trees and rivers are. As far as we know, none of the animals have the ability to ask themselves, “what are those shiny objects above?”
There was a tipping point in our past when we gained the ability to ask that question and unbeknownst to that individual, this is when cosmic quest for our species began, even if that individual lived long before modern humans came to exist.
As it is natural for us to ask questions, it is perfectly natural to not be satisfied until we have the answers, even if that means wrong answers. Throughout the history, humans have seen stars, the Sun and the Moons as deities, long dead ancestors, precious stones in the skies forever unreachable. A long time ago, before the first civilisation, someone might have even guessed that the stars and the Sun are the same kind of objects, just at different distances.
Our minds search for patterns because they have been programmed to do so during the evolution. Recognising a predator camouflaged in its surroundings meant survival. Sometimes it meant seeing things that aren’t there, but often we reaped great benefits from it. Even though there were no predators to jump out of the night sky filled with stars, our ancestors’ minds sought patterns there anyway. They gave names to constellations, they noticed that the seasonal changes and the Sun’s position in the sky were related, they noticed that the Moon changes its shape in regular pattern. These observations, this realisation of patterns gave birth to many things like religions, astrology, calendars and, well, astronomy.
Based on these patterns, humans have been able to predict when to move before the winter came and when to plant seeds, when the rivers will rise and floods destroy the crops. Early civilisations invested time in observing the stars, with nothing more than their eyes and their minds. Earliest known calendar is some 10,000 years old, but with Sumerian culture and their invention of writing, we gained tools to not only observe, but to record changes in movement of celestial bodies.
The oldest systematic observation of stars was done by Babylonians about 3200 years ago as evident in their star catalogues. Their astronomers, priest-scribes mostly, were the first to realise that astronomical phenomena repeat themselves. In centuries to come, they had set the basis for modern astronomy by differentiating between stars and planets, using math to create systems that allowed them to predict motions of planets and repeating patterns of lunar eclipses.
For 21 years, they observed Venus, as is evident from famous Venus tablet of Ammisaduqa, dating from seventh century BC. Babylonians were the first civilisation to realise that Venus is sometimes the first “star” in the night sky after sunset and at another time the last “star” visible before dawn. Before that, we thought morning “star” and evening “star” were two different objects. I ask myself, “did any of those Babylonian astronomers imagine, while watching Venus, that one day human race will send space probes around the planet to find more about it?” Sure, a lot of time has passed and we have achieved things unimaginable to ancient civilisations, but then another thought comes to mind - how will future humans look upon our generation 2700 years from now?
Babylonians found out much just from looking at the stars and jotting down what they have seen, without things we have today, like Google’s search engine, telescopes of various kinds, some of which are in orbit around Earth, without space probes in orbits around other planets. Such was astrology in the beginning - looking with eyes and seeing with minds. Some 2700 years from now, tools that we use will seem primitive to future humans, but the ingenuity is the trait we share with our ancestors and hopefully with our descendants.
In ancient Egypt, astronomy played an important role from the very beginning of their civilisation. It had religious significance for fixing dates of religious festivals. By watching the stars at night, their temple astrologers kept track of the length of the night.
Maybe the most important use for astronomy in ancient Egypt was predicting flooding of the Nile. Their year had 365 days from early on and they used their knowledge to predict when the flooding season begins. It was a very practical way to use astronomy in its infancy and its use has grown tremendously since. Yet, a lot of people see astronomy and cosmology reserved for those with their heads up in the clouds, or far above clouds. I find it to be a shame. In more recent times, astronomy, astrophysics and cosmology departments from time to time experienced budget cuts, often because people in charge couldn’t envision the long-term potential the knowledge in these fields can bring the human race.
Astronomy also played a part in ancient Egyptians’ obsession with life after death. The most famous symbol of Egypt and burial grounds for pharaohs, the pyramids, were often built keeping the position of celestial bodies in mind. One narrow shaft in the Great Pyramid that leads from the main burial chamber to the surface of the pyramid is pointed directly towards the pole star, which at the time the Great Pyramid was built was Thuban in constellation Draco. This is because Egyptians believed that the fixed part of the night sky around which all other stars revolved was a physical gateway to heavens.
Another civilisation took the astronomy to a whole new level. Unlike Babylonians whose astronomy was independent from cosmology, the Greeks began looking for physical and rational way to explain astronomical phenomena and answer the questions about the Universe. They were very interested in figuring out how the Universe was organised and what is our place in it. Some suggested Earth was flat, some that it was cylindrical, some that it was the centre of the Universe, some that it circled an unknown central fire, together with all other celestial bodies including Sun.
Now, when we talk about Greek or Hellenistic astronomy, it is important to keep in mind that after Alexander the Great conquered Persia together with Egypt and Mesopotamia, the Greek culture was spread to these parts of the world and remained dominant long after Alexander was dead. Many astronomers that were neither Greek nor lived in ancient Greece are called Hellenistic. In fact, Alexandria in Egypt and its library were the place to be if you were an aspiring astronomer in centuries after Alexander’s death.
Hellenistic astronomers thus built on the knowledge accumulated by Babylonians and Egyptians. They too were aware that planets are different from stars, that they move. They called them planetes, meaning “wanderer”. Then-known planets, Mercury, Venus, Mars, Jupiter and Saturn were all named after Greek gods. Romans later gave those planets names which they now have, but they are all named after Roman equivalents of Greek gods.
One of the most important Hellenistic astronomers, Ptolemy, was Greco-Egyptian living in Alexandria in 2nd century AD, during Roman reign of Egypt. His Almagest is one of the most influential texts, not only in astronomy, but science in general. In it, Ptolemy supported geocentric system and with Almagest being so influential, geocentric system was dominant view of the Universe for the next 1200 years.
Another astronomer, Aristarchus of Samos, correctly suggested that the Sun was actually the centre and that Earth circled around it. He was right, but had few supporters and his idea was ignored. This was 500 years before Ptolemy. Similar to how science works today, in ancient Greece and Hellenistic world there were philosophers, mathematicians and astronomers with various ideas, learning from each other, criticising one another and stealing ideas from one another. Just like today, influence was important to get your ideas across, but only the right ideas stood the test of time.
Inventor of geography, Eratosthenes, who lived in 3rd century BC, actually measured the radius of Earth with nothing but a stick. He realised that, depending on geographical latitude, the Sun casts shadows of different lengths at the noon on the summer solstice. So, he took a stick and measured its shadow’s length in both Alexandria and Swenet, about 1000 kilometres south of Alexandria. He realised that the surface of the Earth is curved just like sphere’s surface. Knowing the approximate distance between two cities and angles at which the Sun casts shadows in them, he calculated Earth’s circumference surprisingly accurately and from it, Earth’s radius. Yet, people accepted for centuries that the Earth is flat.
Another important Greek astronomer, perhaps the greatest ancient astronomer, was Hipparchus. He was the founder of trigonometry which he combined with his solar and lunar theories to reliably predict solar eclipses. He was possibly the first to do this. Hipparchus is the most famous for discovering that Earth’s rotational axis changes its orientation. This is called axial precession, but historically it was called the precession of the equinoxes, because equinoxes, two events in each year when the Sun is directly over the Earth’s equator, move relative to the fixed stars.
A lot of things we know about Greek and Hellenistic astronomy and cosmology is through quotations in other, later works. It’s no surprise that the right information got lost with time and wrong theories, like geocentric system and flat Earth, stayed dominant for centuries.
Finding answers is not always a straightforward process. With questions getting more complicated, as it is common in astronomy, getting the answer right on the first try is unlikely. The good thing is that, with growth of civilisations and technology, we have more information at our disposal and more people to argue with which answer is right or wrong. Sometime the people who are wrong win the fight and, through their influence, their ideas stay accepted as right for some time, but the human mind doesn’t stop asking questions.
Next time, we’ll talk more about astronomy in ancient China, India and Islamic world, before continuing with discoveries in Western world that led to modern astronomy. I hope you enjoyed this first Cosmic Quest article and that you get to enjoy many similar articles that will follow.