The History of Astronomy

1. The History of Astronomy From Early Man to Newton

2. Early Man • Astronomy is the oldest of the natural sciences and really began with the first questions about observations. • Our distant ancestors looked to the sun and the stars to orient themselves, find their way, foretell the seasons, and for their gods. • Regularity of patterns led to a belief that conscious entities were guiding the movements.

3. Early Man • People believed the gods lived among or were the stars and planets. • Early on, astronomy was intimately tied to agriculture, then religion, divination, prophecy and belief systems. • People believed the movement of the heavens could predict everything! • In many cultures, if astronomers got predictions wrong, they were killed.

4. Early Man • Early astronomy probably dates well before written record, but eventually people started recording events and cycles on bones, cave walls, and seashells. • As the nomadic peoples around the world settled areas and created villages, structures were built to keep track of happenings in the sky. • Thus, the first calendars where born.

5. Early Astronomical Structures • Simple markers/circles made of stone, wood, or earth lines as well as temples and tombs. • Stonehenge (England 2800BC – 1075BC) • Newgrange (Ireland 3000BC) • Big Horn Medicine Wheel (Wyoming, USA 1500AD – 1750) • Nabta (Southern Egypt Ca. 3000BC) • Nazca Lines (Peru 400AD)

7. Ancient China • Oldest established culture w/ recorded astronomical observations • 1st people to record: Solar Eclipse, Super Nova, stellar positions in a catalogue • Astronomy was tied to politics – the ability to predict the future gave power to Emperors • Ability to predict eclipses and comets with astonishing accuracy

8. Ancient Egypt • Pyramids thought to have been aligned with the stars in Orion’s Belt to help facilitate the passage of the pharaohs into the afterlife. • Used the star of Isis (Sirius) to predict the flooding of the Nile for planting crops and to keep track of their year. • Astronomy linked to religious/spiritual beliefs and agriculture. • Many temples and structures built to honor gods and keep track of heavenly movements.

9. The Mayans • Ca. 1000 AD – Yucatan Peninsula, Mexico • Built many structures to keep track of solstices and equinoxes, star alignments, and Venus. • Astronomy was an integral part of life – many ceremonies • Seriously obsessed with Venus – conducted wars and sacrifices based on the planets position and brightness. • Thought Venus more important then the Sun. • Time was the most important concept in Mayan culture. • Dresden Codex – catalogue of observations and tables.

10. The Incas • Astronomy tied to agriculture, created markers to keep track of when to plant crops. • Capital city of Cuzco was originally laid out to mimic the sky. • The Pleiades star cluster was very important and signaled the new year. • Modern day Cuzco built atop ruins of Incan Empire.

11. Ancient Babylonians • Ancient Mesopotamia (middle east) was birthplace of civilization. Nomadic peoples settled this area. • Ancient Sumerians and Babylonians created the first recorded constellations and stories (latter passed on to the Greeks). • Created the Zodiac (12 constellations the sun, moon, and planets pass through each year) • Astronomy also used for agriculture, time keeping, predicting eclipses. • Invented degree system used for positions in the sky. • Venus cycle and identity.

12. The Ancient Greeks • Because much of the recorded history of ancient civilizations prior to the Ancient Greeks has been destroyed or lost, many sources begin with the history of astronomy in Ancient Greece. • Greece was hotbed for astronomical theory and observation as well as philosophy, mathematics, ethics, drama, politics and other scholastic pursuits. • Part of success lies in extensive written records of previous cultures, which the Greeks built upon.

13. The Ancient Greeks • Approached Astronomy not with the mindset of worship or divination, but to try and understand the universe. • “the mysteries of the universe are mysteries because they are unknown, not because they are unknowable” – Thales Miletus (624-547BC) • Pythagoras claimed the underlying rules of the universe to be mathematical. • Largely believed in geocentric model • Earth was motionless and center of universe • Occam's Razor before William of Ockham

14. The Ancient Greeks • Surrounded by celestial sphere • Explained how stars, etc. moved around the Earth • Transparent crystalline sphere embedded with stars, moved around Earth • Seven “wanderers” lay on spheres between Earth and outermost sphere

15. Aristotle (384-322BC, Greek) • Universe = 2 parts: corrupt and changeable Earth, perfect unchangeable heavens. • Geocentric view due to lack of parallax (shift of stars). • Proved the Earth spherical using sailing ships and eclipse shadows. • Had many followers, and was known as the “authority” on learning for nearly 2000 years!

16. Aristarchus (310-230BC, Greek) • First suggestedheliocentricmodel – sun centered. • Used simple geometry to calculate distance to sun from Earth and Moon. • Later calculated relative sizes of same bodies (lacked accuracy). • Concluded Sun was much larger and more distant than Moon. • Ideas largely ignored due to influence of Aristotle.

17. Eratosthenes (276-195BC, Greek) • Calculated the circumference of Earth by using the angle of noon day sun at two Egyptian cities and geometry. • Credited with almost exact measurement of Earth circumference.

18. Hipparchus (190-120BC, Greek) • The greatest O.A. • Created first star catalogue. • Almost 850 stars divided into 6 brightness categories still in use today. (Hipparchus’s Mag. Syst.) • Measured length of year within minutes and predicted eclipses. • Discovered the precession (wobble) of Earth. • Calculated accurate distance to moon. • Invented trigonometry.

19. Claudius Ptolemy (85-165AD, Greek) • 13 volume series called Almagest (“great work” a culmination of his own ideas and work of past thinkers). • Created a mathematically based geocentric model for the universe. • Explained retrogrademotion (even with Geocentric model) • Ptolemaic Systemlasted for 13 centuries and was eventually adopted by Catholic Church

20. The Ptolemaic Universe • System of wheels w/in wheels to describe planetary motions and preserve geocentrism. • Planet lay on small circle called epicycle, which in turn was centered on the orbit around Earth called the deferent. • Eventually errors occurred overtime, prompting astronomers hundreds of years later to adjust constants and add epicycles – was still the model accepted by the ruling authority, the Roman Catholic Church.

21. Nicholas Copernicus (1473-1543, Polish) • The Revolutionary • Challenged the Ptolemaic System, by concluding that the Sun was at the center of the universe in his book “On the Revolution of the Celestial Orbs”. (printed at death) • Copernican Revolution – a complete overthrow of previously accepted authoritative doctrine – along side Martin Luther and other revolutionaries. • Kept circular orbits (only mistake). • Better explanation of retrograde motion.

22. Galileo Galilei(1564-1642, Italian) • The defender. • Built his own telescope and made many stunning discoveries which forever changed our view of the universe. • Dynamic lunar surface (imperfect heaven), Phases of Venus (must orbit source of light, changing heaven), Moons of Jupiter (Earth not center of all motion), Sunspots (imperfect heaven), many more stars in than previously thought. • Evidence supported Copernican view, GG was outspoken about this.

23. GG. • Took on the “man” during four Inquisition interrogations. • Defended his ideas even when threatened with torture. • Bruno, another supporter of the C.S., burned at the stake in Rome.

24. GG. • GG was eventually forced to recant the ideas in his published works and admit his errors. • “E pur si muove” (still, it moves.) • House arrest for life. • Church finally absolved GG in 1990, 348 yrs later. Victory.

25. Tycho Brahe (1546-1601, Danish) • The observer. • Very proud nobleman, eccentric to say the least. Metal nose (duel over a math formula in college). • “Kept” a little person named Jepp (Tycho thought him to have physic powers). • Prized pet elk, which upon visiting another nobleman on Tycho’s behalf met a sad end…

26. TB • Wealthy enough to have his own castle observatory an island off the Danish coast. • Created observational tools and made very tedious observations of the night sky for 20 yrs. • Accurately measured 777 stellar positions using only sights.

27. Johannes Kepler (1571-1630, German) • The Analyst • Worked for/with Tycho and eventually inherited all of Tycho’s observations/data. • Used Tycho’s work to develop the 3 laws of planetary motion. • Used correct ellipses instead of circles for orbits.

28. JK • Law of Elipses – 1 planets’ orbits are elliptical, with the sun at one focus pt. • Law of equal areas – 2 a line from the sun to the planet sweeps out equal areas in equal time. • P2Y = a3au , orbital period squared (yrs) equals the distance of the planet from the sun cubed (au).

29. Sir Isaac Newton (1643-1727, British) • Physicist, astronomer, theologian, mathematician, natural philosopher, and alchemist among other things. • Dvlp. the 3 laws of motion, invented calculus, reflecting telescope, made his own apocalypse prediction. • Dvlp. the universal law of gravity.

30. Newton • Newton couldn’t define gravity, but observed/measured the effects of gravity which he then quantified as the Force of Gravity. • The development of this law lead to an understanding of orbital motion of the moon and planets. • Final blow to geocentrism. • Lead us into space.