The Early History of Astronomy

1. The Early History of Astronomy The ancient people saw seven celestial bodies moving through the stars; Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn.

2. Five of these objects appeared to “wander” through the constellations. These objects were considered to be special stars, which they called planets.

3. Ptolemy (100-200 AD) • Determined the positions of about 1,000 bright stars. • Summarized the geocentric model of the universe, which stated that the Earth is motionless and everything revolves around it.

4. Retrograde Motion • The problem was that the planets seem to loop backwards and if they were making perfect circles around the earth that wouldn’t happen. • We can this strange phenomenon retrograde motion

5. In the Earth-centred model, planets orbit on epicycles– wheels whose centers– are attached to the planets’ celestial sphere. (placing epicycles upon epicycles.)

6. Aristarchus 310-230 BC • He proposed that all of the planets, including Earth revolved around the Sun, and that the Earth rotates on its axis once a day. This is the heliocentric model.

7. Sun centered model • The sun centered model of the solar system accounts for the wacky movement of the planets. • In this model retrograde motion is an optical illusion which makes it seem as if planets go backward

8. Sun centered model • What is actually happening is that the planets are moving in different sized orbits at different speeds, so they catch up and pass each other, making it look like they are moving in opposite directions when its really the same

9. Video Link for Retrograde Motion • http://honolulu.hawaii.edu/distance/sci122/SciLab/L2/MarsRetroMany.html • http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

10. Homework • Over the years, space has been used for various things. • List (brainstorm) as many ways as possible that humans have used the celestial bodies over the years. • You and a partner must make a poster to present your information. • Due Monday