Introduction to Astronomy

The Great Medieval Debate: Do we live in a Geocentric (Earth-Centered) or

Heliocentric (Sun-Centered) System?

Learning GoalsStudents will:1) Develop scientific argumentation skills

(students will use Earth-based observations to prove the commonly understood notion that the sun is in the center of our universe).

2) Understand that ancient humans could only use Earth-based observations to understand that our solar system is heliocentric.

Success CriteriaStudents will display learning goals by:1) Using research skills to obtain information.2) Collecting data to disprove the points

suggested by geocentric theory.

AstronomyI don’t care what your grade 6 teacher told you – but the Earth is in the center of the Universe and all other celestial bodies (including the sun, the planets and the stars) revolve around the Earth!

AstronomyIf you don’t believe me, I’ve got proof!

It’s all just common sense – all you have to do is watch the sky during the day and night and even collect data for several weeks.

Let me list the observations you will make:

Astronomy1) Over the course of the day we

watch the sun rise in the east, move across the sky and set in the west – the sun is obviously revolving around the Earth!

2) Similarly – during the day and night we can watch the moon revolve around the Earth.

Astronomy3) If we watch the stars

carefully at night, we notice that they circle around us. A camera taking a long exposure photograph of the sky will produce a picture with star trails. This proves that the positions of the stars are moving around us from East to West.

Star trails photographed in a long term exposure near an astronomical observatory

Astronomy4) The Parallax

EffectDepending upon the position of the Earth in its orbit, nearer stars should be in different positions relative to more distant stars. Have you ever observed this? I haven’t!

Astronomy

A simple test of the parallax effect is to place your thumb in front of your face and observe an object with your left eye only. Now switch to using your right eye only. The object will be in a different position relative to your thumb. We can see that the building appears to be in a different place relative to the thumb in the two pictures. The same thing should happen as the Earth travels in orbit. More distant stars should appear to be in different positions relative to closer stars or planets.

Astronomy5) If we plot the position of planets carefully

at night, we notice that they also move but at a different (slower) speed than the stars.

6) If the Earth were orbiting the Sun and rotating on its axis, wouldn’t we be swept away by the wind and then fly off into space?

7) God created the Earth on the first day but didn’t create the Sun and Stars until the fourth day. God created man in his own image and put humans as the masters of the universe and therefore must have placed humans in the central location in the universe

Prove or Disprove my Statement!

1. Using evidence that can be obtained by looking at the sky, argue against my claim that the Earth is in the Center of the Universe (Geocentric Theory).

2. OR IF YOU REALLY WANT TO - AGREE WITH MY STATEMENT – but you must add to my argument! (Aristotle is on my side as well.) I would suggest that you prove that the Heliocentric Theory makes no sense

We will now head to the library for a research session

1. Find evidence that disproves my Geocentric (Earth-Centered) Theory and supports your Heliocentric (Sun-centered) Theory. OR

2. Agree with my Theory (Suggest that either a lack of evidence or my strong logic proves that I am right)Collect evidence from the library and record

your facts on paper. NO plagiarizing! You must put the evidence into your own words and be prepared to discuss the data in front of the class.

YOU MUST UNDERSTAND THE DATA IN ORDER TO BE ABLE TO ARGUE YOUR POINT!!

1) Sun and Moon revolve around Earth2) Stars revolve around Earth3) The Parallax Effect is not observed.4) Planets move across sky – only slower5) We’d fall off the Earth if it was moving in

orbit6) God created us and put us in the center of

the Universe

This data is included on the Argument Summary

Here is the summary of my evidence:

What I need to get from you:

1) A completed argument summary – a page of written evidence is sufficient

2) HOWEVER MUCH GREATER VALUE WILL BE GIVEN TO THOSE WHO:

a) provide diagrams or astronomical charts to help prove your point (make them big enough to show the class)

b) add clear written support of the arguments you find – you can add extra pages if you wish!

3) I will not make life easy for you! Photographs taken from spacecraft (a picture of the planets revolving around the Sun, photos from Satellites, pictures from the Mars Rover etc.) make too simple an argument. Remember – 100 years ago scientists such as Claudius Ptolemy, Galileo and Copernicus did not have the luxury of spacecraft and were able to make good arguments on both sides of this debate. What evidence could an Earth-bound observer use to convince me that I am wrong!

4) Reference your work – write down the names of books or web sites that you used to gain information

5) YOU MAY WORK WITH A PARTNER – BUT IF YOU DO I WILL EXPECT MORE WORK!

6) Prepare to defend yourself IN A SCIENTIFIC ARGUMENT!

7) Remember that simple textbook or internet pages showing photographs are not sufficient. It is likely that none of you can produce the background facts that support the Sun-centered theory shown in these pictures. I need the written explanations to go with your ideas

Astronomy

Need a few research hints to get you started?

Here are some keywords:

Heliocentric GeocentricCopernicus Aristotle PtolemyGalileo ParallaxRetrograde Motion