Presentation on theme: "The Roots of Astronomy Already in the stone and bronze ages, human cultures realized the cyclic nature of motions in the sky. Monuments dating back to."— Presentation transcript:
1Early Views of the Solar System (With thanks to Mark Ritter & John Bloom)
2The Roots of AstronomyAlready in the stone and bronze ages, human cultures realized the cyclic nature of motions in the sky.Monuments dating back to ~ 3000 B.C. show alignments with astronomical significance.Those monuments were probably used as calendars or even to predict eclipses.
3StonehengeConstructed: 3000 – 1800 B.C.Summer solsticeHeelstoneAlignments with locations of sunset, sunrise, moonset and moonrise at summer and winter solsticesProbably used as calendar.
4Big Horn Medicine Wheel (Wyoming) Examples All Over the WorldBig Horn Medicine Wheel (Wyoming)
5Examples All Over the World Caracol (Maya culture, approx. A.D. 1000)
6Ancient AstronomersNo written documents about the significance of stone and bronze age monuments.First preserved written documents about ancient astronomy are from ancient Greek philosophy.Greeks tried to understand the motions of the sky and describe them in terms of mathematical models.
7Ancient Greek Astronomers Models were generally wrong because they were based on wrong “first principles”, believed to be “obvious” and not questioned:1. Geocentric Universe:Earth at the Center of the Universe.2. “Perfect Heavens”:Motions of all celestial, ethereal bodies described by motions involving objects of “perfect” shape, i.e., spheres or circles.
8General Greek Principles of Science Nature can be understood(Not just randomly occurring phenomena)The diverse behavior observed in nature is held together in patternsTendency to“Save the Phenomenon”
9Euclid ~ 600 BC What he got right: What he got wrong: Predicted solar eclipsesMoon shines due to reflected sunlightUniverse explainable by ordinary knowledge and reasonWhat he got wrong:Thought Earth was a flat, rotating diskThought water was a fundamental element from which all other matter derives
10Pythagoras ~ 530 BC First to suggest that Earth is a sphere First to suggest that Earth is a sphereOne of the earliest advocates of a geocentric solar system:Earth at center, surrounded by system of concentric, rotating, transparent spheresBodies attached to spheres in this order:Moon, Mercury, Venus, Sun, Jupiter, Saturn, stars
11Philolaus ~ 410 BC (student of Pythagoras) Suggested Earth moves around a central fire(NOT the Sun)What were his new ideas???
12Ancient Greek Astronomers Eudoxus (409 – 356 B.C.):- Model of 27 nested spheresAristotle (384 – 322 B.C.), major authority of philosophy until the late middle ages:- Universe can be divided in 2 parts:Imperfect, changeable EarthPerfect Heavens(described by spheres)Aristotle expanded Eudoxus’ Model to use 55 spheres.
13the Aristotelian universe ~ 340 BC In ancient times philosophers argued from first principles, things that were accepted as “obviously” trueSeveral important ideas ruled the ancient world…
14Aristotle ~ 340 BC first: the earth was round gave 4 reasons for earth’s roundness:Symmetry: the sphere is a perfect shapeElements have their natural places: Earth’s pieces fall naturally to Earth’s center, pressing it into a spherical shape (circular reasoning!)Shadow: Lunar eclipse shadow (Earth’s shadow on Moon) is always circular (what if Earth were a circular disk?)North Star: Polaris gets higher in the sky the further north one goes
15second: the earth was located in the center of the cosmos! third: the heavens were perfect, the earth imperfectall the cosmos traveled in perfect circles around usPlato pushed this, his student, Aristotle adopted ithe gave us the Aristotelian way of looking at the cosmos…
16geocentric universe with all the heavenly objects moving in uniform circular motion Aristotelian concepts dominated ancient ideas about the universe for thousands of years…Two major themes here:1) our place in the cosmos2) the character of planetary motion
17Aristarchus ~ 240 BCRotation of Earth on its own axis accounts for daily motion of starsEarth revolves around Sun in a yearly orbitHe had it right before 200 BC!But his ideas failed to catch on…
18Eratosthenes ~ 235 BCCalculated Earth’s radius to within about 5% accuracy!Basic method:Measured shadow lengths at two different cities directly North-South of each other (Syene and Alexandria)Calculated Earth’s circumference and radius using geometryCentral angle = 7.5 degrees, 500 miles from A to S, times 48 = 24,000 miles;Actual angle = 7.2 degrees, 500 mi x 50 = 25,000 miles.
19Ptolemy ~ 120 AD great ancient astronomer of the 2nd century wanted to put it all this orbital motion into a mathematical modelfinal effort to “Save the Phenomenon”no significant changes for 1300 years!Ptolemaic view = geocentric view
20why did they think we were in center anyway? popular worldviewthe Sun appears to rise, transit the sky, and setit doesn’t feel like we are moving!and there was the problem of…
21parallax, the apparent motion of an object b/c of the motion of the observer if we were going around the sun, the background stars should change position!(they do, but not a lot since they are so far away)Ancients didn’t have telescopesHad no idea how far away the stars were
22planetary motion was difficult for the ancients to explain planets (wanderers) would suddenly backtrack!called retrograde motion
23Ptolemy tried to explain it with epicycles (little circles - blue) on deferents (big circles - white)all in an attempt to keep the Aristotelian (geocentric) view of the cosmos
24all Ptolemy’s attempts to mathematically explain Aristotle's universe were put together in a book preserved by the Arabs, Al Magisti, then translated into Latin, The Almagestbut unknown to them it was all wrong! enter…
25Copernicus ~ 1500 ADa Polish monk, Mikolai Kopernik (Lt. Nicolaus Copernicus) rediscovered the heliocentric model of the universebut being for heliocentrism was being against Aristotle, and against the Church!After Aristarchus!
26De Revolutionibusfinished in 1530, Copernicus wrote De Revolutionibus Orbium Coelestrium (“on the revolution of the celestial orbs”)he didn’t give permission for its publication until he was dying
27most important idea?he put the sun (Sol) in the center!
28with the sun at the center the whole universe was simplified and elegant, and could explain things like retrograde motionwe, moving faster on the inside, see other planets “seem” to move backwardbut!…
29Copernicus insisted on circular orbits! so he had to come up with his own epicycles so it worked better…
30his model was incorrect but his hypothesis with the sun in center was rightbut without a telescope it couldn’t be substantiated with evidenceAND his circle obsession meant it couldn’t predict things very wellAND it upset people because their whole universe changed!so it wasn’t accepted for a long time
31Tycho Brahe ~ 1500sthe greatest pre-telescopic observational astronomer(also known for his fake nose and bladder problem)
32in 1572, he saw a supernova which he called a new star it showed no parallax, so he deduced it to be a part of the starry spherebut the star sphere was “perfect and unchanging”!!!
33so the new star challenged Ptolemy and Aristotle Brahe wrote a book on it called De Stella Novawhich got the notice of lots of people and made him famous…
34Danish king Frederick II gave him island of Hveen to build an observatory (Uraniburg)
35here Tycho shows off the latest mural quadrant with tools like these (notice no scopes) he observed the heavens and took over 20 years of data!
36Tycho had his own version of what was going on neither Ptolemaic nor CopernicanEarth was at center, but all the other planets went around the sunTychonic view
37Tycho ended up in Prague and hired some new assistants to help prove his system was correct one of the assistants was Johannes Kepler
38Johannes Kepler (1571 – 1630) Kepler had a not-so-fun life born in 1571 in Germany, he was poor, had an absent father, was sickly, had a nasty mother, etc., etc.
39a Copernican, Kepler even wrote a book Mysterium Cosmographicum which tried to prove that all the planets were built with regular solids as spacers!
40joining Tychoeventually, after being persecuted for being a Protestant, he headed for Prague to work for Tychothen Tycho died…so, Kepler took all of Tycho’s work to finish the Rudolphine Tables himself
41with all of Tycho’s data, Kepler tried to find out how the planets really moved he discovered that Mars moves in an ellipse, not a circle!and it traveled at different speeds!
42he wrote a lot after this and in 1619 published The Harmony of the Worlds in which he said that the radii of the planets’ orbits are related to their periodsall this led to his three fundamental laws of planetary motion…
43Kepler’s three laws of planetary motion first law relies on the ellipse – an oval drawn around 2 pointspoints called foci (sing: focus)semimajor axis (a) = half the longest diametereccentricity (e) is half the distance between foci divided by the semimajor axisa circle is an ellipse with e = 0greater e more ellipticalGreater e = more elliptical, less symmetric/circular
44Kepler’s First Law (Law of Ellipses) states that all planets travel in ellipses with the sun at one focus
45Second Law (Equal Areas-Equal Times) planets sweep out equal areas in equal times translation: they go faster when closer to the Sun
46Third LawT2 = R3states that the closer a planet is to the Sun the shorter its “year”T = period in Earth yearsR = distance in AUsgiven one, you should be able to find the otherKepler never knew why his laws worked, just that they did
47the Rudolphine Tablesfinally, in 1627, Kepler finished the R Tables, a precise model of planetary motion(notice Tycho as part of the pillars of astronomy)a contemporary of Kepler was…
48Galileo Galilei (1594 – 1642)helped push science to a new level…
49telescopic observations GG had an academic upbringing and was quietly Copernicanit was the telescope that pushed him over the tophe used this recent invention to examine the sky and gather evidence for the heliocentric view
50he immediately published his findings in Siderius Nuncius (The Sidereal Messenger) here he reported several big discoveries…
511: The Moon was not perfect!!! remember Aristotle said everything in the heavens was perfect?but the Moon looked sort of like Earth!!!
52Major Discoveries of Galileo Surface structures on the moon; first estimates of the height of mountains on the moon
532: There were lots of stars up there (many more than were previously supposed) the Milky Way (and the rest of the heavens) is substantial, like the earth, not ethereal
543: He saw four little “stars” near Jupiter these points of light were going around Jupiter!but they weren’t supposed to!!!! they should have been left behind!!!So, not everything orbits the Earth…and, if Jupiter can move and keep its “moons” so could Earth
55Major Discoveries of Galileo Moons of Jupiter(4 Galilean moons)(What he really saw)Rings of Saturn(What he really saw)
56Major Discoveries of Galileo 4: He saw that the sun had spots (proving that the sun is not perfect!), and that it rotated
575: He observed that Venus went through phases (including “full Venus”) So what? it can only have all phases if it goes around the sun, not the Earth!
58but even with all this evidence people were still upset some didn’t even look through the telescope!The Catholic Church, still in love with Aristotle, told Galileo to be quietit was in 1629 that he wrote his great defense of the Copernican way…
59Galileo’s Dialogue it was an imaginary debate between three friends: Salviati (pro-Copernican) Sagredo (indifferent) Simplicio (pro-Ptolemy)problem: Simplicio presented the Pope’s view of things … bad move!
60Galileo was brought before the Inquisition charged with not shutting upcondemned to life imprisonmentnote: what Copernicus and Kepler and Galileo taught and discovered didn’t contradict the Bible…it contradicted people’s interpretations, traditions, and worldviews
61The Birth of Modern Science in trying to understand the skies in the 16/17 century, modern science was bornnothing more than a logical way of observing, studying, and thinking about naturescientific method (Roger Bacon, 13th century)cause and effect (Francis Bacon, 17th century)et al…
63Isaac Newton and orbital motion by now we have a new outlook on the universe and new ways to study it allperfect time for this guy to show up…
64Isaac NewtonIsaac was very smart, raised in England, educated at Trinity, but…during the Black Plague of 1665 went home to Woolsthorpewhile there he thought through his laws of motion…
65which he wrote about in his Principia from the work of all the great guys before him he gave us three laws of motion which we still usehe realized the same force that brings an apple to the Earth keeps the Moon in orbitand those other things must be pulling on us, too
66he figured if something has mass it has gravity mass is how much stuff/matter something hasweight is the force that something exerts because gravity pulls on it
67He also realized that the distance plays a huge role and is an inverse square relationdouble the distance and gravity decreases by 4x.
68know the relationships… the force of gravity attracting two objects is proportional to their masses, but inversely proportional to the squares of their distances
69orbital motion here’s why satellites orbit celestial bodies throw something hard enough and the Earth will curve out of the wayit will “fall” foreverthat is being in orbitorbital motion