Rhythms of the heavens

1. Rhythms of the heavens

2. Getting started • To what extent are we aware of basic observations made with the unaided eye? e.g. movements of the Sun, Moon, planets, stars. • Do we connect these observations with our modern view of the solar system?

3. 3500 years ago • Babylonians noticed that the planetary ‘wanderers’ kept to a narrow band of night sky which repeated each year.

4. Retrograde motion • The word ‘planet’ means wanderer. • The apparent backwards loops made by the planets are called ‘retrograde motion’.

5. 2500 years ago • Greek civilisation flourished. • Greeks made good estimates of the radius of the Earth and the size and distance of the Moon. • Models built to describe the observed motion of the Sun, Moon and planets. All were based on perfect circles.

6. 120 AD • A Greek called Ptolemy devised a model which had the Earth near the centre. • Ptolemy invented epicycles to account for retrograde motion. • Sailors used this model for navigation for 14 centuries.

7. Ptolemy Ptolemy’s Model

8. 16th century • Copernicus (a monk from Poland) removed the Earth from the centre of the solar system to make it just another planet. • The Copernican scheme still used epicycles.

9. Copernicus’ Heliocentric Model Copernicus

10. Can you guess who didn’t like this idea? • This was not a popular move with the Christian church! • The term ‘revolution’ was born!

11. Late 16th century • Tycho Brahe (Danish) made regular and precise measurements of the positions of the Sun, Moon and planets over a period of 20 years. • Johannes Kepler (German assistant to Tycho Brahe) developed a geometrical explanation for the solar system based on ellipses. Brahe Kepler

12. Kepler showed that the orbit of Mars was elliptical

13. Kepler’s ideas developed from extremely accurate measurements made by Tycho Brahe were able to establish the supremacy of the heliocentric model.

14. 17th century - Galileo • Galileo (Italian) used observations made with the newly invented telescope to provide further support for the heliocentric model. • Galileo discovered Sun spots and thus showed that the Sun rotated. • Galileo observed the phases of Venus providing evidence that Venus orbits the Sun. • Galileo observed moons around Jupiter. • Galileo developed important ideas about motion.

15. Galileo A replica of Galileo’s Telescope

16. 17th century - Isaac Newton • Newton was able to build on the work done by Kepler, Galileo etc to compile a coherent set of ideas to explain all the motions within the solar system and on Earth. This Newtonian mechanics still forms the basis of most of our mechanics calculations nearly 350 years later. • NASA used Newtonian mechanics to put a man on the Moon.

17. Newton

18. Explaining retrograde motion using the heliocentric model

19. Retrograde motion again. • Now launch the file 20L ‘Retrograde motion of Mars’ from within Activity 20S Software Based ‘Retrograde Motion’. You should now understand why retrograde motion comes about with a heliocentric model of the solar system. • You may be able to find other simulations of retrograde motion on the Internet.

20. Acknowledgements • The contents and scanned images have been taken from Jon Ogborn and Rick Marshall 2008 Advancing Physics A2 (IOP Publishing) which should read in conjunction with this presentation. • Slide 7: Image of Ptolemy - kenoath.wordpress.com • Ptolemy’s model - danieljklotz.files.wordpress.com • Slide 11: Image of Tycho Brahe - ircamera.as.arizona.edu • Image of Johannes Kepler - astronomy.nmsu.edu • Slide 15: Image of Galileo - ircamera.as.arizona.edu • Image of telescope - galileotelescope.org • See the original as well as Galileo’s finger at the Institute and Museum of the History of Science in Florence, Italy! • Slide 17: Image of Newton - www.physics.mun.ca • This PowerPoint was compiled by John Mascall of The King’s School, Ely in April 2009.