Medieval Renaissance

The Dark Ages:

1. Explain why the knowledge of the Ancient Greeks gradually became inaccessible to scholars during the Dark Ages.

   A merger of the church and state led to a decline in science.

2. What is the example provided in the lecture which demonstrates the lack of knowledge about the sky during this time period?

   The church developed a system of education based on scripture rather than pagan Greek Philosophers. You cannot read it in a literal context.

The Rise of Islamic Astronomy:

1. Describe how the knowledge of the Ancient Greeks was preserved during the Dark Ages. Why were Islamic scholars interested in the astronomical knowledge of the Ancient Greeks?

   During the Dark Ages, Ancient Greek knowledge was oppressed and people translating it could be charged with treason. Islamic scholars were interested in the astronomical knowledge of the Ancient Greeks because the Qur’an encourages knowledge of the sky for timekeeping**.**

2. Why is Ptolemy's astronomy textbook known as "The Almagest"?

   Ptolemy’s “Mathematical Principles” was translated in Arabic and then to Latin “The Almagest” meaning “The Greatest.”

3. What can we tell about the star “Alpha Centauri” based on its name, and who named the stars in this format?

   • Alpha Centauri is a star system, and the name “Alpha” means the brightest of the stars (beta, gamma, etc.)

   • Arabs named stars in this format because they were creative with naming stars visible to the naked eye.

4. Why are the names of bright stars typically Arabic in origin? Describe one of the examples provided in the lecture or reading material.

   • Bright stars are typically Arabic in origin because of the Golden Age of Islam. They named stars based on the stories of the constellations.

   • Ex. Betelgeuse comes from bat al-jawza (The Giant’s Shoulder)

Early Renaissance Astronomy:

1. What was the importance of Regiomontanus’ translation of The Almagest?

   Regiomontanus’ translation of The Almagest was directly from Greek to Latin (not the usual Arabic to Latin), including commentaries and annotations that allowed people to understand the Ptolemaic Universe without the complicated mathematics.

2. Whose cosmology did the medieval Church adopt, and why? Was it geocentric or heliocentric?

   The medieval Church adopted Ptolemy’s geocentric cosmology.

The Copernican Model:

1. What 2 features of the Ptolemaic model led Copernicus to suspect that the model was incorrect?

   • Ptolemy’s geocentric model was unable to predict the position of planets with good enough accuracy

   • ???

2. According to Copernicus, what do the planets orbit around, what is the shape of their orbits, and do they move at constant or non-constant speeds through space?

   • According to the Copernicus, the planets orbit around the Sun in a constant, circular motion.

3. In the Copernican model, what are the 3 components of Earth's motion?

   • The Earth has a daily rotation about its polar axis which explains the daily motions of the sky.

   • The Earth has an annual circular orbit around the Sun explains the Sun’s annual cycle.

   • The Earth’s axial tilt at 23.5 degrees explains the precession of the equinoxes and the seasons.

4. What was Copernicus' correct explanation for retrograde motion?

   • Retrograde motion was an apparent motion of the planets relative to their distance from the Earth, rotation around the Sunm and the Earth’s own rotation. When the Earth “overtakes” an outer planet’s orbit, it appears to move backward (retrograde) relative to the stars.

5. In the Copernican model, when do planets appear to slow down and increase their brightness, and why? Does this match what we observe in the sky?

   • In the Copernican model, planets appear to slow down and increase in brightness when Earth overtakes them in orbit, causing them to enter retrograde motion and appear closer to Earth (because the Earth is closer in proximity), which matches what we observe in the sky.

6. What was Copernicus' correct order of the planets?

   • Mercury, Venus, Earth, Mars, Jupiter, Saturn

7. In the Copernican model, what is the explanation for the different motion of Mercury and Venus compared to Mars, Jupiter and Saturn?

   • Mercury and Venus are much closer to the Sun and are in between the Sun and the Earth, which is why they move differently from Mars, Jupiter, and Saturn, which are all behind the Earth and further from the Sun.

Copernicus’ De Revolutionibus:

1. When Copernicus compared the orbital periods of the planets with their orbital radii in his heliocentric model, what did he find?

   He found out that because planets like Jupiter and Saturn are further from the Sun, they take longer to make a full orbit around it.

2. What is the (shortened) name of Copernicus' famous book in which he presented his heliocentric cosmology?

   De Revolutionibus/On the Revolutions is the short version of De Revolutionibus Orbium Coelestium/On the Revolutions of the Heavenly Spheres.

The Early Observations of Tycho Brahe:

1. What planetary event did Tycho Brahe witness in 1563? Describe what causes this event and how it appeared in the sky. What did this event motivate Tycho to do, and why?

   • Tycho Brahe witnessed the Supernova 1572.

   • A Supernova occurs when massive stars die in extraordinary explosions, lighting up the sky before disappearing.

   • This motivated him to observe annual stellar parallax.

2. What discovery did Tycho make about the supernova of 1572 ("Tycho's Star"), and how did it contradict Aristotelian beliefs about celestial bodies? Is "Tycho's Star" still visible without a telescope? How can we tell today that a supernova really did occur in the Cassiopeia constellation?

   • This event convinced Tycho that the phenomenon belonged to the heavens, meaning the heavens were changing in contrary to Aristotle’s fixed picture of the universe.

   • Tycho’s Star is no longer visible without a telescope because Supernovas disappear. We know a supernova occurred in the Cassiopeia constellation because the remains of a supernova are still there.

3. What sort of observations did Tycho make from his observatories on the island of Hven, and why were these observations so valuable?

   • Tycho observed a supernova and attempted to observe stellar parallax. The supernova encouraged him to observe stellar parallax and believe that the heavens were not fixed like Aristotle said, and stellar parallax prevented him from believing in heliocentrism.

Tycho’s Search for Stellar Parallax:

1. What is parallax? Describe how parallax would affect a photograph of a stop sign if you took the photograph from two different locations.

   • Parallax is the apparent shift of an object relative to its background due to the change in the observer’s point of observation.

2. Describe how parallax affects our view of the stars. Can we see stellar parallax with the naked eye? Why/why not?

   • Because of the Earth’s shift, parallax occurs in our view. Stellar parallax happens when stars shift due Earth’s motion through space and the closer a star, the more it shifts. You cannot detect parallax with the naked eye. The closest star, Proxima-Centauri, has a parallax angle of 0.76 arc seconds while the human eye can only perceive angles larger than 1 arc minute.

3. Explain (very generally – no calculations necessary) why Tycho’s search for stellar parallax led him to believe that the Earth is motionless.

   • Because Tycho could not see stellar parallax, he assumed the Earth was not moving at all or the stars are too far.

4. What is the definition of an 'Astronomical Unit'?

   • Astronomical Unit: 1 AU is the average distance between the Earth and the Sun, around 150,000,000,000km

The Tychonic System:

1. Describe the motion of the Sun, Moon, stars and planets in the Tychonic system.

   • In the Tychonic system:

     • The Earth is fixed at the centre

     • The Sun, Moon, and stars orbit Earth

     • The planets orbit the Sun

2. Does the Tychonic system explain the 3 features of apparent planetary motion? Why/why not?

   • No, the Tychonic system does not explain the 3 features of apparent planetary motion because while it incorporates a version of epicycles to explain retrograde motion, it does not account for why planets change brightness and speed explicitly.

3. Explain how Tycho’s observations of the Great Comet of 1577 led him to conclude that the crystal orbs do not exist. Why did this conclusion make the Tychonic system more believable?

   • Tycho measured the distance to a comet using the parallax method, proving that comets belonged to the celestial realm. If they belong to the celestial realm, then it had to intersect the Sun’s crystal orb without shattering it. This proved that there are no crystal orbs, supporting Geocentrism.