Topic 1 Visible light and the Solar System

1.1 Describe how ideas about the structure of the Solar System have changed over time, including the change from the geocentric to the heliocentric models and the discovery of new planets


The ideas of the structure of solar system have evolved over time.  We will discuss Plotomey, Copernicus and Galileo models which are the requirements of examiners.

Ptolemy(c90-168AD) an astronomer of Greek created his geocentric model. In his model the earth was considered as the centre of the solar systme and all the planets and the sun were orbiting around it as shown below.

geocentric model

Later Nicolaus Copernicus (1473-1543) came up with the idea of heliocentric model (helio means Sun, so heliocentric means Sun as centre) as shown below.

heliocentric model

As shown in above diagram, Sun is at the centre but Planets farther than Saturn are not shown this is because at that time telescopes were not good enough to see beyond Saturn and therefore the Solar system remained undiscovered.

Galileo Galilei (1564-1642) who made improved telescope opened new vistas for astronomical discoveries. He discovered that Jupiter had four moons which were orbiting Jupiter itself. From this observation he concluded that not everything is revolving around the Earth and thus went against geocentric model of the solar system.

Later up to the begning of 18th Century moons of Saturn kept discovering in which Christian Huygens Played an important role. 

In 18th Century Uranus was discovered by William Herschel. He later discovered four of Uranus' moons and two of Saturn's.

In 19th Century Neptune was discovered by Galle and Le Verrier.

Moons of Saturn and other planets were also kept discovered. Some of those moon's were considered as planets. Such as in 1841 there were 13 Planets and in 1851 they were reduced to 8 Planets.

In 1930 Pluto was discovered as ninth Planet, however, in 2006 it was relegated to the level of drawf planet thus removed from the position of 9th Planet of Solar system.