The Early History of The Early History of AstronomyAstronomy

The ancient people saw The ancient people saw sevenseven celestial bodies moving through the celestial bodies moving through the stars; Sun, Moon, Mercury, Venus, stars; Sun, Moon, Mercury, Venus,

Mars, Jupiter, Saturn. Mars, Jupiter, Saturn.

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

Ptolemy (100-200 AD)Ptolemy (100-200 AD)

Determined the Determined the positions of about positions of about 1,0001,000 bright stars. bright stars.

Summarized the Summarized the geocentric model of geocentric model of the universe, which the universe, which stated that the stated that the EarthEarth is motionless and is motionless and everything revolves everything revolves around it.around it.

Retrograde MotionRetrograde Motion

The problem was that the planets seem to loop The problem was that the planets seem to loop backwards and if they were making perfect backwards and if they were making perfect circles around the earth that wouldn’t happen.circles around the earth that wouldn’t happen.

We can this strange phenomenon retrograde We can this strange phenomenon retrograde motionmotion

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

Aristarchus 310-230 BCAristarchus 310-230 BC

He proposed that all He proposed that all of the planets, of the planets, including Earth including Earth revolved around the revolved around the SunSun, and that the , and that the Earth rotates on its Earth rotates on its axisaxis once a day. This once a day. This is the heliocentric is the heliocentric model.model.

Sun centered modelSun centered model

The sun centered The sun centered model of the solar model of the solar system accounts for system accounts for the wacky movement the wacky movement of the planets.of the planets.

In this model In this model retrograde motion is retrograde motion is an optical illusion an optical illusion which makes it seem which makes it seem as if planets go as if planets go backwardbackward

Sun centered modelSun centered model What is actually What is actually

happening is that the happening is that the planets are moving in planets are moving in different sized orbits different sized orbits at different speeds, so at different speeds, so they catch up and they catch up and pass each other, pass each other, making it look like making it look like they are moving in they are moving in opposite directions opposite directions when its really the when its really the samesame

Video Link for Retrograde MotionVideo Link for Retrograde Motion

http://honolulu.hawaii.edu/distance/sci122/SciLab/L2/MarsRetroMany.html

http://www.lasalle.edu/~smithsc/http://www.lasalle.edu/~smithsc/Astronomy/retrograd.htmlAstronomy/retrograd.html

HomeworkHomework

Over the years, space has been used Over the years, space has been used for various things. for various things.

List (brainstorm) as many ways as List (brainstorm) as many ways as possible that humans have used the possible that humans have used the celestial bodies over the years.celestial bodies over the years.

You and a partner must make a poster You and a partner must make a poster to present your information.to present your information.

Due MondayDue Monday