Brainlag PlusHow the Earth-centred model gave way to the Sun-centred one and the evidence that did it, what telescopes add, why some telescopes must be in space, and what each part of the electromagnetic spectrum shows us.
Two models of the solar system
This lesson is for Edexcel (1PH0).
AQA and OCR do not ask about it, so skip it if you sit one of those.
- Geocentric (geo = Earth): the Earth is at the centre, and the Sun, Moon, planets and stars orbit it. Ptolemy set it out in detail around AD 150. It matched everyday experience: we do not feel the Earth move, and the Sun seems to cross the sky.
- Heliocentric (helio = Sun): the Sun is at the centre, and the Earth is one of the planets orbiting it. Copernicus published it in 1543.
Planets sometimes seem to drift backwards across the night sky for a few weeks. To explain this, the geocentric model needed extra small circles (epicycles) on top of the orbits, which made it complicated. In the heliocentric model it happens naturally, as the Earth overtakes a slower outer planet.
The rest of this lesson and its 10 practice questions are in Plus.
Screen 1 of 5, free to read.
- 10 exam-style questions, marked as you go, each with a worked solution
- Anything you get wrong is saved to your flashcards