The History of Astronomy. From Early Man to Newton. Early Man. Astronomy is the oldest of the natural sciences and really began with the first questions about observations.
The History of Astronomy
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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!
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.
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.
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.
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
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.
Nicholas Copernicus (1473-1543, Polish)
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.
Galileo Galilei(1564-1642, Italian)
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.
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.
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.
Tycho Brahe (1546-1601, Danish)
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…
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.
Johannes Kepler (1571-1630, German)
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.
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).
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.
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.