-
500 BCE
Eudoxus and Aristotle's Models of the Universe
In around 500 BC, Eudoxus, a Greek scientist, proposed the very first model of the universe, a geocentric model (suggesting that the Earth was at the centre of the universe and the Sun and planets revolved around it). In 400 BC, his theory was supported by philosopher Aristotle, who used evidence such as the spherical nature of the Earth to construct a model featuring 55 spheres rotating around the Earth. -
300 BCE
Aristarchus and Eratosthenes' Theories
In the third century BC, Aristarchus measured the distance between the Earth and the Sun using trigonometry, and discovered the extremely large size of the Sun and the long distance between the two bodies, and used this as evidence to propose a heliocentric (Sun centred) model of the universe, which wasn't initially accepted. Soon after, Eratosthenes measured the circumference of the Earth to be approx. 46,000 km, further deepening his society's understanding of the universe. -
150 BCE
Ptolemy's Developments
Later, astronomer Ptolemy developed on Aristotle's geocentric theories, observing that planets did not appear to orbit the Earth in perfect circles and sometimes appeared to travel backwards. He reasoned that they moved in circles - or epicycles - as they orbited the Earth, as shown in the diagram below. -
1543
Copernicus' Heliocentric Model
In 1543, the first widely accepted model of the universe as heliocentric was proposed by the Pole Copernicus. He concluded that the Sun was at the centre of the universe, and that the Earth and other planets in the solar system revolved around it at uniform speeds with epicyclical movements. -
1570
Brahe's Observations
In the late 16th century, the Dane Tyson Brahe greatly contributed to scientific understanding of the universe through his record of extremely accurate observations and ideas. He concluded that the planets revolved around the sun, which in turn revolved around the Earth. He also disproved previous theories that the universe was unchanging as he witnessed two supernovas, resulting in the creation of new stars in various constellations. -
Kepler's Theories
Using evidence recorded by Brahe and other astronomers, German Johannes Kepler argued that planetary orbits were based on geometric shapes, and eventually concluded that they revolved around the Sun in elliptical motions, and that the closer they were to the Sun the faster they completed their orbits. His work also helped to explain the apparent retrograde motions of Mars' orbits. -
Galileo's Observations
Using telescopic technology he constructed himself, astronomer Galileo Galilei observed a number of phenomena in the solar system, including the moons of Jupiter, the moon's craters, the phases of Venus and more, and conclusively disproved the geocentric model of the universe. He also helped in developing the theory of relativity, which helped to explain why we do not feel the movement of the Earth as it revolves around the Sun, popularising the heliocentric model of the universe. -
Newton's Proof
Physicist Isaac Newtown developed his famous three laws of motion, and mathematically proved the existence of gravity, developing his own universal gravitational law which conclusively proved the heliocentric model of the solar system. -
A Larger Universe
In the 19th century, many believed that the universe was confined to just Earth, the Sun and some other planets in the solar system. However, discoveries by Bessel, Wilhem von Struve and Galle made it clear that the universe was far, far larger, with millions of other planets, stars, solar systems, galaxies and nebulas. By the end of the 19th century, most astronomers supported the "steady state" theory, which proposed that the universe was homogenous, infinite in size and static or unchanging. -
Big Bang Theory
Today's understanding of the universe can largely be attributed to the development of the Big Bang theory, proposed initially by Georges Lemaître. Contradicting the steady state theory, it proved that the universe was formed by a massive explosion of a single particle, and has expanded at a rapidly accelerating rate ever since this explosion. Over time, it was supported by a range of evidence, including the cosmic microwave background and the observation of "red shifted" stars.