Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

PHYSICS · Stage 7 · Chapter 5: The Earth in Space

Physics 5.8 Changing ideas 3: modern astronomy — Galileo, Kepler and Telescopes

5 min read 7 parts Lesson 8 of 11

0%read
Lesson summary

Physics 5.8 Changing ideas 3: modern astronomy — Galileo, Kepler and Telescopes — Alhussan International Academy — Physics (Stages 7–9) notes: Describe the heliocentric model, the telescope evidence for it and how scientific explanations develop.Five planets — People before 1600 …

  • Celestial spheres
  • New evidence
  • Copernicus
  • Features of the model
  • Simplicity
  • Publication

Part 1 of 7Ideas before 1600

  • Five planetsPeople before 1600 had only ever seen five planets, along with the Sun and the Moon.
  • Celestial spheresThey were happy with the explanation that astronomical objects were carried on celestial spheres around a central Earth.
  • New evidenceOnly new evidence, which came with the invention of the telescope, would change people's view of the Universe.

Part 2 of 7The heliocentric model of Copernicus

1Copernicus3 points
— Born in Poland in 1473, before telescopes existed, he promoted the heliocentric model in Europe.
  • "Helio" means Sun in Greek.
  • He did not invent the idea: Aristarchus produced a Sun-centred model about 1200 years earlier, and Al-Biruni suggested it about 500 years earlier.
  • Al-Biruni thought it was not possible to prove that the Earth was moving.
2Features of the model
— The Sun was at the centre, the planets orbited the Sun, and the Moon orbited the Earth.
3Simplicity2 points
— The model explained the motion of the planets much more simply.
  • Scientists look for the simplest explanation of their observations.
  • If explanations become very complicated, scientists look for a simpler one.
4Publication2 points
— Copernicus found it difficult to discuss the model openly because the Earth at the centre was part of religious belief.
  • He feared persecution, so his book appeared as he died.
  • It was published in Latin, which few people understood.

Part 3 of 7Galileo and the telescope

1Telescope
— Invented in the Netherlands in 1600; Galileo Galilei, an Italian scientist, made his own in 1609.
2Moons of Jupiter3 points
— Galileo saw four objects orbiting Jupiter rather than the Earth.
  • These are the four biggest moons of Jupiter, now called the Galilean satellites.
  • They were evidence that not all objects in the Universe orbit the Earth.
  • Galileo thought planets orbit the Sun just as moons orbit Jupiter.
3Sunspots1 point
— Galileo saw dark spots on the Sun.
  • This showed that astronomical objects such as the Sun are not perfect.
4Retrograde motion
— Planets seen from the Earth appear to move backwards because they orbit the Sun at different speeds.

Part 4 of 7Galileo's publication and its consequences

  • Public support — Unlike Copernicus, Galileo talked about his model in public.
  • Church opposition — Church leaders in Rome tried to make him take back his claim, but he refused.
  • Book of 1632 — It showed how the heliocentric model explains the evidence more simply than the geocentric model.
    • It was published in Italian, which many people understood.
  • Imprisonment — He was kept imprisoned in his house until he died in 1642.
  • Acceptance — After his death the heliocentric model gradually became accepted.

Part 5 of 7Kepler and the shape of orbits

  • Elliptical orbitsJohannes Kepler used careful observations to show that planets travel in ellipses, not perfect circles.
  • SpeedPlanets move faster when they are nearer the Sun.
  • Better fitThese changes made the heliocentric model match observations accurately.

Part 6 of 7How scientific ideas change

1New evidence
— Explanations change when new evidence, such as telescope observations, is found.
2Simpler explanations
— A simpler explanation is more likely to be accepted.
3Why an explanation may be unknown3 points
— A scientist may not know that someone has already developed an explanation.
  • It may not have been published.
  • It may be in a book that has not yet reached them.
  • It may be written in another language.
4Modern picture1 point
— The Sun is the centre of our Solar System, not of the Universe.
  • Astronomers have built a model of a Universe much larger than the Solar System that contains galaxies.

Part 7 of 7Key scientists compared

ScientistContribution
AristarchusSun-centred model about 1200 years before Copernicus
Copernicus (born 1473)Promoted the heliocentric model as a simpler explanation of planetary motion
Galileo (telescope 1609)Moons of Jupiter and sunspots; published support for the heliocentric model
KeplerPlanets travel in elliptical orbits, faster when nearer the Sun

Last updated: