1. The Origin of Modern Astronomy

2. What scientists have contributed to our understanding of astronomy…
A timeline

3. The Babylonians

4. The Babylonians 3000 BCE 1792-1750 BCE Identified constellations
Developed a calendar tied to the recurrence of certain astronomical events
BCE
Venus Tablet was inscribed
They believed that the movements and positions of planets with respect to the constellations could influence the fate of Kings and nations

5. The Chinese
2500 BCE
Developed the concept of a 365-day year based on what appeared to be the Sun’s annual journey across the background stars
They believed an eclipse took place when a dragon attacked the Sun, trying to consume it
They would then gather people to scare the dragon
This lead to the development of the Saros cycle where the Sun, Moon, and Earth are aligned every 18 years and 11.3 days

6. The Egyptians The Pyramids
Contain prayers which reference the pharaoh joining the circumpolar stars, which neither rise nor set, and therefore live eternally
Archaeologists speculate they may have been observatories

7. The Europeans Stonehenge Built between 2800 – 1550 BCE Believed to be
An astronomical observatory
A computer of astronomical phenomena

8. The Greeks Anaximander – 610–545 BCE Theorized
The world and everything in it were derived from an imperceptible substance apeiron (unlimited)
Earth floated freely in space at the center of the universe
The stars were fiery jets
The sun was a chariot wheel whose rim was hollow and filled with fire

9. Thales – 624–546 BCE Credited as the founder of Greek science
Proposed the first model of the universe that did not rely on supernatural forces

10. Anaximenes of Miletus Pythagorus – 580-500 BCE Theorized
Aer (air or vapor) was the most basic form of matter and was also the substance that formed the life spirit of animals, the soul of humankind, and the divine essence of the gods
Pythagorus – BCE
Earth was a globe fixed within a sphere that held the stars

11. Anaxagoras – 500-428 BCE Theorized The Sun was a large, red-hot body
The moon was much like Earth, complete with mountains and ravines
Solar eclipses were caused by the passage of the moon between the Sun and Earth

12. Plato – 427-347 BCE Eudoxus – 408-355 BCE
Proposed that celestial bodies moved about Earth at a constant speed and followed a circular motion with Earth at the centre - geocentric model
Asserted that heavenly motion must be in perfect circles and that heavenly objects reside on perfect spheres
Eudoxus – BCE
A student of Plato
Attempted to explain the RETROGRADE MOTION of the wandering stars (planets)
Charted the northern constellations
Created a model that used nested spheres

13. Aristarchus of Samas – 310-230 BCE
Aristotle – BCE
Put the Earth at the centre of the universe
Expanded on the idea of the spheres put forward by Eudoxus
Aristarchus of Samas – BCE
Theorized
Earth is not at the center of the universe, instead it orbits the Sun while also rotating – heliocentric model
This theory however was rejected

14. Hipparchus – 190-120BCE Claudius Ptolemaeus – 127 – 145 CE
Sorted the stars into 6 orders of brightness
Along with Aristarchus, measured the Earth- Moon distance by timing lunar eclipses.
Claudius Ptolemaeus – 127 – 145 CE
Known as Ptolemy
Added to the geocentric model a system of complex deferents and epicycles
Deferents – large circular orbits centered on Earth
Epicycles – small circles whose centers travel around the circumferences of the deferents
There were 80 deferents and epicycles

15. Ptolemaic Model

16. The Middle East
Abu ‘Abd Allah Muhammad Ibn Jabir Ibn Sinan Al-battani Al-harrani As-sabi’ – CE
Also known as al-Battani
Refined the calculations of the length of the year and the seasons
Al-Sûfi – CE
Meaningfully discussed the comparative brilliance of the Stars

17. The Europeans Nicolaus Copernicus – 1473-1543 CE 1514
Was asked by the Catholic Church to improve the accuracy of the current calendar
Rediscovered the heliocentric model
He argued that all the motion we see in the heavens is the result of Earth’s daily rotation on its axis and yearly revolution around the Sun, which is motionless at the center of the planetary system
Held onto the idea of epicycles and constant circular motion
Proposed that stars were very far away

18. Why was this new idea considered such a big deal?
It required a shift in understanding in two areas

19. The universe had to be a much bigger place than previously imagined
Stars appeared in the same positions with the same apparent brightness. Why didn’t they change?
Copernicus explained that the starry celestial sphere had to be so distant from Earth that changes simply could not be detected

20. Why do things fall?
Aristotle had explained that bodies fell toward their natural place, which was the center of the universe. Aristotle of course had believed that the Earth was the center of the universe, explaining why all things fell towards the ground.
Copernicus had no explanation to counter this argument.

21. Tycho Brahe – CE
Considered the best naked-eye observer of all time.
Nov 11, 1572 observed a very bright star (SN 1572) in the constellation Cassiopeia
This star showed no daily parallax, thus it was far away
The star did not change position relative to the fixed stars over several months
This star is now classed as a Supernova

22. Was able to show that the Stars existed way beyond the distance of the moon
He was convinced that the planets must orbit the sun, but was unable to develop a satisfying model
He believed in geo-centrism, and furthered the work of Ptolemy
He developed the Tychonic system
The sun circles the Earth
The 5 planets circle the sun

23. Johannes Kepler – 1571-1630 CE Worked for Brahe Highly religious
Believed in the Heliocentric model
Attempted to find a physically realistic model for Mars’ orbit
This finally lead him to discard the circular orbit

24. Galileo Galilei – CE
Built a telescope in 1609 which he used to:
Explore the imperfect surface of the moon covered with craters, “seas”, and features that looked like the surface of Earth
See the surface of the sun was blemished with sun spots and that these changed position from day to day
He concluded that the sun was rotating making a complete revolution in 1 month
His observations helped solidify the idea of a heliocentric model and Kepler’s orbits, which he published in 1610
Brought before a Catholic Church inquistion in 1616.
The church judged the work to be heretical and banned it
1632 he published a comparison of the Ptolemaic and Copernican models where the Copernican view came out the winner
1992 he was formally vindicated by the Pope

25. Sir Isaac Newton – CE
Proposed three Laws of Motion and the Law of Universal Gravitation