Intro to AstroLesson 4: The Revolution

Challenge of the Day• Prove it activity!

Movie Debrief• David Christian tells us why stories change. Can you

think of a time when you changed a story because of new information?

• Can you understand why Ptolemy saw the Earth as the center of the Universe based on what you can see of the Sun, the Moon, and the stars?

• What major shift occurred with the Copernican view of the Universe?

How do we know what we know?• We know these things to be true now, but

how did people know 2,000 years ago?

• It is important to review the proof, the science and the evidence that has gotten us to our present understanding

Scientific Revolutions

• What does progress look like?

• Science goes through a process, claims are forwarded, defended, refuted, even died for

• The great minds of astronomy made these accomplishments on their own through hard work, pain, and meticulous learning

How do we know the earth is round?• Aristotle: Studied a lunar eclipse and the

shape the shadow of the earth made on the moon

• What shape does it make?

• How does that provide evidence for a spherical earth?

Continued• Aristotle also made a very keen

observation of a ship sailing away towards the horizon

• What happens?

• How does this provide evidence?

• Picture of sailing ship

Continued

• When Aristotle traveled he noticed that you can see different star constellations in different places

• Would this be possible if the earth was flat?

Eratosthenes • Video

How do we know the Earth revolves around the Sun?

• Aristarchus: 280 BC

Aristarchus

• Did measurements using trigonometry concluding that the Sun is much larger than the earth

• Also observed that the stars don’t move, this could be evidence in favor of geocentrism, but Aristarchus didn’t think so

• Parallax, instead the stars a very far away

Ptolemy

• 2nd century, Ptolemy came up with a model of the solar system that had the earth at the center

• He mapped the known the planets, calculated the time it took them to orbit the earth

• His model was the accepted model of the solar system for almost 1,400 years

• It was wrong but was it bad science?

Motion of the Planets

•Geocentrists: We see the planets move across our sky, and we stand still.

•The planets must be orbiting around us!

•How do we know the difference between the planets and the stars?

Retrograde Motion

• The planets move continuously across our sky, but at some point, something very weird happens

• They start to move backwards for a period of time

• Why?• This was the central mystery of astronomy for

many centuries

Retrograde Motion

• Ptolemy offered an explanation to this phenomena in his model

• http://astro.unl.edu/classaction/animations/renaissance/ptolemaic.html

• It was wrong, but was it bad science?

Another Model Appears• Not until the 1500’s did Ptolemy’s

model get challenged, and it did by an astronomer named…

• Nicolas Copernicus

• Made official claims that were being put forth since Aristarchus

• http://astro.unl.edu/classaction/animations/renaissance/retrograde.html

• http://astro.unl.edu/classaction/animations/renaissance/ptolemaic.html

• http://astro.unl.edu/classaction/animations/renaissance/venusphases.html

Copernicus• Copernicus provided a radical model of the solar system,

one that placed the SUN at the CENTER

• He, like Ptolemy, provided calculations for the orbits of the planets, the seasons, and the solstices

• He even offered an explanation for why the planets move backwards

• http://astro.unl.edu/classaction/animations/renaissance/retrograde.html

The Church• The Catholic Church, the primary

political and social power at the time, did not like Copernicus’ idea

• Why? Ideas?

The Church• The Scriptures say that the earth is,

and shall forever be, “unmoved”

• By taking the earth out of the center of the solar system, it makes our role in it seem less important, less “central”

Galileo• The dawn of the telescope!

• Article