The universe contains everything that exists, including the Earth, planets, stars, space and galaxies – all matter, energy and even time. Its basic constituent is luminous matter, i.e. galaxies, which are collections of billions of stars.
1. From Geocentric to Heliocentric Model
Before astronomical instruments were invented, people thought that the Earth is the centre of all the objects in space. This was the geocentric model. Later the heliocentric model (helios = Sun) placed the Sun at the centre of the solar system.
| Astronomer / Event | Period | Contribution |
|---|---|---|
| Ptolemy (Greek) | 2nd Century | Held the geocentric model |
| Aryabhatta (Indian) | 5th Century | Held the geocentric model |
| Nicolaus Copernicus (Polish) | Later | Proposed the heliocentric model, with the Sun at the centre |
| Invention of the telescope | 1608, in the Netherlands | Created a revolution in astronomy |
| Johannes Kepler | Early 1600s | Proposed three laws of planetary motion, using the data of his mentor Tycho Brahe |