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School Physics Notes: Astronomy 1. History of models of our Solar System

ASTRONOMY: 1. A history of models of our Solar System - geocentric and heliocentric models

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The importance of the scientific work of Copernicus and Galileo

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1. A history of models of our Solar System

How has the explanation, theory and model of the Solar System evolved through time?  

The 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 geocentric model theory - wrong!

The sun, moon, planets, and stars i.e. everything you could see, all orbited the Earth in a series of concentric circles.

So the Earth was considered to be the centre of everything in the Solar System.

An orbit is the path one object moves around another object (held in orbit by gravity).

They also considered the orbits to be perfect circles.

This model originates from ancient Greek civilisation 2000-2500 years ago and lasted for 1500-2000 years.

Ancient astronomers didn't have telescopes to make accurate observations to test out any other model.

What they observed was the Sun and moon moving across the sky in the same way every day and every night and assumed they moving in a perfect circle around the Earth.

They did observe the apparently wandering of the planets - the word planet comes from an ancient Greek meaning 'wanderer', but this did not lead to a questioning of the geocentric model

Prior to ~1500s this was the accepted model of the Universe from the time of the ancient Greeks.

The heliocentric model - correct!

From the 1500s onwards and with the help of telescopes, evidence was mounting up to indicate that the planets were orbiting the Sun - the heliocentric model, but not in perfect circles.

The Sun is now considered to be the centre of our solar system.

We now recognise that the Earth and other planets are moving around our Sun in elliptical orbits.

Initially the Sun was considered as the centre of the Universe, but of course we now know it is now only the centre of our solar system.

Astronomers such as Copernicus working in the mid-16th century, were making observations and calculations to explain the movement of the planets without the geocentric model and that a heliocentric model fitted the data better.

Copernicus published his heliocentric theory and calculations in 1543, just in time, two months before his death!

Galileo’s observations of Jupiter, using the telescope, provided evidence for the heliocentric model of the Solar System - initially it provided evidence that not everything revolved around the Earth.

Galileo, in the early 17th century, working with the newly invented telescope, found his view of the 'universe' in conflict with that of the Catholic Church, especially after discovering moons orbiting around the planet Jupiter, which meant not everything orbited the Earth and the geocentric model was flawed.

One piece of Galileo's evidence came from observing the moons moving around Jupiter with his newly invented improved telescope of 1609, he therefore observed objects moving around with Jupiter, which clearly could not be moving around planet Earth.

Initially Galileo thought four stars were surrounding Jupiter, but he figured out they were moons of Jupiter because of their movement - they moved along with Jupiter and were observed in different positions around it - therefore showing that all 'heavenly' bodies were not moving around the Earth.

The Catholic Church was not too impressed by a scientific model challenging the religious view of how our 'universe' works.

Over the following centuries more evidence for the heliocentric model increased, helped by the technological advances in astronomy eg improved telescope designs.

From the early 20th century onwards, it was recognised that our solar system is just one of billions of systems with a central star in a galaxy and that there are billions of galaxies that make up everything - the Universe!


Keywords, phrases and learning objectives for astronomy

A history of geocentric and heliocentric models of our solar system important work of Copernicus Galileo

  • Be able to 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 geocentric model: The sun, moon, planets, and stars ie everything, all orbited the Earth in a series of concentric circles.
      • This model originates from ancient Greek civilisation 2000-2500 years ago and lasted for 1500-2000 years.
    • The heliocentric model: The Earth and other planets orbited our sun -then considered as the centre of our universe.
      • Astronomers such as Copernicus working in the mid-16th century, were making observations and calculations to explain the movement of the planets without the geocentric model and that a heliocentric model fitted the data better.
        • Copernicus published his heliocentric theory and calculations in 1543, just in time, two months before his death!
      • The Catholic Church was not too impressed by the scientific model challenging the religious view of how our 'universe' works.
    • Our contemporary model: The 8 major planets, minor planets and asteroids orbit the Sun in slightly elliptical orbits (our 'Solar System'), but our Sun is just one of millions-billions of stars in our galaxy (we see part of it as the 'Milky Way') and in turn the observable universe itself contains billions of other galaxies.
    • Be able to discuss how Galileo’s observations of Jupiter, using the telescope, provided evidence for the heliocentric model of the Solar System.
      • Galileo, in the early 17th century, working with the newly invented telescope, found his view of the 'universe' in conflict with that of the Catholic Church, especially after discovering moons orbiting around the planet Jupiter, which meant not everything orbited the Earth and the geocentric model was flawed.

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