1- Beginning at the beginning in cosmology

We will start with a ‘word’, a ‘person’ and a ‘terminology’, that are related to the story of cosmology. 

The word is GEO.It originates from the Greek word GE which means ‘earth’. Therefore Geology means earth+logy. (‘logy’ means something that is heavy and moves slowly,) so the word ‘geology’ means big/slow-moving earth. In this example the ‘slow’ doesn’t mean the speed of the planet, but the way the rocks evolve over a long time period. And so geology describes the study of the earth’s rocks and minerals.

Similarly, Geo-graphy means a ‘graph’ of the earth, and is used to describe writing about the earth. When used in terms of astronomy, ‘geo’ is used to describe things in space that are related to the Earth – such as – Geo-Stationary-Orbit which would be a satellite orbiting in a stable position around the Earth.

We are going to use one of these words in our discussion in a minute – geocentric. It describes something where the ‘Earth’ is at the centre i.e. ‘centric’. In this example imagine the Earth is at the centre of the universe and all the planets orbit around it, therefore we would describe it as a geocentric universe; a universe that revolves around the planet Earth.

The person is Ptolomy. His name pops up here and there in history but it’s hard to appreciate who he really was. He is the first person we will associate with the history of cosmology because he gave the world a very important thing; he defined what was the basic belief in Astronomy – that the Earth was the centre of the universe and that there was a geocentric universe.

The terminology is CE and BCE.We will talk later of how distance and time is measured in space but first look at how it is done here on Earth. The advanced world, namely Europe, became Christianised at an important time in world history called The Renaissance.It was a time when culture, art and literature turned medieval Europe into an advanced civilisation. Russia, in the very East of Europe, was the only nation that did not have a renaissance because it was still run by barbarians who cut themselves off from the West.

In Europe they changed to the Gregorian calendar, whereas in Russia they kept the Julian calendar. In Europe they became Christians under the Holy Roman Empire with the pope as its head, whereas in Russia they became Orthodox Christians under the Greek/Byzantine Empire with the Tsar at its head. The pope at that time was actually the Caesar of Rome, and in Russia the word ‘Tsar’ comes from Tsarista, derived from the word Caesar.

So it turned out that both east and west of Europe had a calendar (which was 13 days apart) and they had a Christian religion. ‘Christ-ian’ meaning that it was founded on ‘Christ’ and therefore year zero in both calendars was the time when Jesus Christ was born.

Any time in history before year zero was referred to as B.C. which means Before Christ. Time after year zero was referred to as A.D. Anno Domini, (Latin words meaning Anno: year and Domino: Lord – the dominant one.) So A.D. means ‘The year of the Lord’. If you read old books you might see for example: Isaac Newton was born on 4th January in the Year of Our Lord 1643. OR Isaac Newton was born on 4th January in 1643 AD.

These days it is appreciated that other civilisations and religions may not wish to measure their time according to Jesus Christ or the Christian religion. So year zero remains the same but the terminology has changed; the time since year zero is referred to as the Common Era (CE) and time before year zero is Before the Common Era (BCE).

We will now discuss below and expand briefly on the differences and similarities between the universe and the cosmos and also between astronomy and astrology.



Claudius Ptolemaisis better known as Ptolomy and the name is pronounced TOLLO-MEE. He cemented the geocentric universe and his ideas dominated astrological thinking for 1,400 years until his theories were challenged by those that believed in a heliocentric universe; one that is centred around the Sun.

He was a Greek astronomer who lived in the second century CE. He worked at the famous library of Alexandria. It’s still there today called the ‘Biblioteque’. He set the form of the Ancient Greek universe in his book The Almagest.The theory in his book is known as the Ptolemaic Theory. With the Earth at the centre, all the other planets revolve around it, including the sun. Except for the stars, they were fixed and never moved.

Ptolemy’s view came from the beliefs of other Greeks before him. All the ancient peoples before Ptolomy believed the Earth lay at the centre of the universe and many thought that it was flat. The Greeks took things a little further because Pythagoras had been a Greek that invented geometry (the study of Earth measurements.) Ptolemy applied Pythagoras geometry to space and was able to calculate very precisely the positions of the planets; in those days planets were referred to as ‘heavenly bodies’.

The Greeks believed that a circle was the perfect geometric shape. All of the ancient civilisations believed that the Earth was at the centre. Many also believed that the Earth was flat otherwise things would fall off it. When Ptolemy wrote The Almagest he brought together the ideas from the past, not just his own.

For example, the ancient Mesopotamians laid down the oldest astronomical records and first described the stars in constellations well before 2000 BCE. Yet in his book, Ptolemy used that information to devise his own constellations, of which we still use today as the signs of the zodiac. His book used all the wisdom of the past, along with Greek geometry to understand how the stars were placed in the sky and provided the means to calculate the planetary positions. Therefore positions of the planets in the future could also now be calculated.

One thing that did contradict Ptolemy’s view was that his own calculations showed that the Earth could not be at the exact centre of the Sun’s orbit around it. This was not resolved for hundreds of years until the sixteenth century when Nicolaus Copernicuspublished a book in 1543 CE called On the revolution of heavenly spheres(De Revolutionibus orbiumcoelestium) in which he presented the heliocentric modelof the universe in much the same way as Ptolemy had done in 150 CE with his geocentric model in The Almagest.

Since the days of the ancient Egyptians and other advanced ancient civilisations, astronomy and astrology was the same thing. This was because before the more scientific studies came, the heavens were based on gods and superstitions. So a bright star could mean something good or a comet seen could mean the crops were going to fail. Ptolemy separated them in another important book called Tetrabiblos.In this work he explained his belief that the heavenly bodies affected events on Earth, in other words he wrote about astrology.



Ptolomy’s books defined astronomy and astrology. They allowed astronomy and astrology to use calculations to plot the planetary movements and interpret how they affected humans. For astrology, a point in time, say a birthday, was required and the positions of the heavenly bodies could be shown at that time and interpreted.

His ideas went unchallenged for about 200 years until another Greek philosopher Aristotle built on them. It was an Indian man called Aryabhata (in 499 CE) who wrote in his book the Aryabhatiya, that the stars were not stationary, it just seemed that way because the earth was rotating. But Ptolemy’s ideas by and large survived up until Copernicus.

Now let us just touch very briefly on the terms universe and cosmos. They are basically interchangeable. However you do find sometimes an explanation given that ‘universe’ refers to the chaotic state and that cosmos refers to the ordered state. What they are saying is that when the moment of creation occured, it was like a big explosion, and that all the planets and stars are like the debris from a bomb. What the term ‘cosmos’ explains is that whenever you find chaos, it sort of orders itself.

So if there was a big bang then everything must be scattered randomly, yet we find that planets are arranged neatly in orbits around stars which also are arranged in galaxies and in turn those galaxies are spread evenly. Therefore although the terms universe and cosmos are one and the same, sometimes ‘universe’ refers to the chaotic universe and ‘cosmos’ refers to the orderly universe. When we use the term ‘cosmology’ we are talking about the scientific study of both the chaotic and orderly, it is the study of everything which was mainly started in the 1960s CE due to major discoveries, such as the ‘background radiation’ which we shall encounter further on.