ASTRONOMY 2021/2022 | Astro Midterm Exam Guide 2022.

ASTRONOMY 2021/2022 | Astro Midterm Exam Guide 2022. The present day search for like in the universe differs from the ancient speculations is an important way: ○ while ancient people could do little more than guess about the possibility of finding life elsewhere, we can now study this possibility with the powerful methods of modern science // The ancient debate about life beyond Earth ● Scholars in ancient Greece debating over whether there was life beyond Earth tells us a major change in human thinking was underway ● Ancestors attributed solar finding to the actions of Mythological beings ○ Evident as our planets are named after Greek Gods ● Greek efforts marked the first attempts to understand the universe through methods closely resembling the ones we use in science today ○ Greek scholars sought rational explanations of what they could observe around them ● People in the past studied the sky because it affected their day to day lives ○ Moon’s connections to tides = people living near the sea ○ Sun & stars served as a time tracking tool = agriculture //Early Greek Science ● Greek philosophers moved human understanding of nature from mythological → rational ○ None of these ideas rose quite to level of modern science as Greeks tended to reply more on pure thought and intuition than on observations or experimental tests ● THALES: ○ First person to ask “what is the universe made up of” without resorting to supernatural solutions ○ OWN GUESS: universe consisted of water and that Earth was a flat disk on an infinite ocean 3 Major Innovations in Greek thought → Modern Science 1. Tradition of trying to understand nature without relying on supernatural explanations ● They were free to think creatively because they were not trying to prove preconceived ideas ● As a result, worked communally and debated and tested each others ideas ● Tradition of challenging virtually every day new ideas remains a distinguishing feature of modern science 2. Mathematics in the form of Geometry ● Use of mathematics to help explore the implications of new ideas remains an important part of modern science 3. Understanding that an explanation about the world could not be right if it disagreed with observed facts ● Willingness to discard explanations that simply don’t work is a crucial part of modern science //Geocentric Model ● Greatest greek contribution: ability to synthesize points above and create models ● Model: conceptual representation whose purpose is to explain and predict observed phenomena ○ Eg. model of climate uses logic, math, and known physical laws to explain how the climate works ● Scientific models may not fully explain all our observations of nature, but they are close ● Greeks constructed conceptual models of the universe to explain what they observed in the sky ● ANIMAXANDER: suggested that heavens must form a celestial sphere around the earth and guessed that Earth’s surface must be curved ○ Celestial sphere: complete sphere ○ Wanted to explain the way the northern sky appears to turn around the North Star each day ○ Incorrectly guessed that the Earth was a cylinder and not a sphere ● PYTHAGORAS: adopted a spherical Earth because they had interest in mathematical perfection and they considered a sphere to be geometrically perfect ● ARISTOTLE: cited observations of Earth’s curved shadows the Moon during lunar eclipses as evident for a spherical Earth ● Greeks adopted a geocentric (Earth Centric) model: of the universe with the spherical Earth at the center of a great celestial sphere ○ Did this way before columbus colonized america and thought he figured out that the earth was round ● ERATOSTHENES: fairly accurately measured Earth’s circumference in 240BC //Planetary Motion ● The sun, moon, and 5 planets are visible to the naked eye ○ Mercury, Venus, Mars, Jupiter, Saturn ○ These 7 are originally referred to as planets ○ Planet = wanderer (greek word) ○ Our 7 day week is directly traceable to the fact that these 7 planets are “visible” from heaven ● The movement of these planets convinced the Greeks that there had to be more to the heavens than just a single sphere surrounding Earth ○ Sun revolves every year ○ Moon revolves every month (MOONTH) ● While the planets usually move east → relative to constellations, sometimes they reverse course and go backwards ○ Apparent retrograde motion: when a planet seems to reverse course and go backwards ○ Periods of retrograde last from a few weeks to a few months depending on the planet ● Seemingly erratic planetary motion was not easy to explain with rotating spheres cause Greeks generally accepted Plato’s “Heavenly perfection” which demanded that all heavenly objects move in perfect circles ● PTOLEMY: came up with a model of planetary motion ○ Ptolemaic model: reproduced retrodage motions by having planets move around Earth on small circles that turned around larger circles ■ Planets following this “circle-on-circle” motion motion traces a loop with the backward portion of the loop mimicking apparent retrograde motion ■ This model correctly forecasted future planetary positions within a few degrees of arc ■ Mars never changes direction, it only looks like it does ○ Put some of the circles off-center to get his model to match his observations ○ When arabs transcribed his work into a book they called it “almagest”= the greatest work //An Alternative Model ● ARISTARCHUS: suggest earth goes around the Sun ○ Made measurements that convinced him that Sin is much larger than the Earth ■ Maybe he just thought it was more natural for the small thing to travel around the big thing ○ Had little success convincing everyone of his findings as it seemed inconsistent with observations of stellar positions in the sky ● Aristarchus Inconsistency ○ If sun was in the middle, earth would be closer to different portions of the celestial sphere at different times of the year and the stars on that part would appear more widely separated ■ Greeks observed no such shift ○ Knew there were only 2 possible ways to explain the lack of a shift 1. Earth was center 2. Stars were so far away, we could not detect shift with eyes ● Seemed unreasonable to Greeks that stars could be so far ● Stellar parallax: annual shifts in stellar position ○ Provide concrete proof that Earth goes around Sun //Roots of Modern Science ● Greeks rejected the correct idea of earth around sun, but it came to the attention of COPERNICUS: who took the idea and ran with it and made it what we use now //POSSIBILITY OF LIFE BEYOND EARTH ● Greeks considered the word “world” to include the Earth and heavenly spheres that surround it and were open to the possibility that other worlds might exist Composition of the World ● Thales ○ Water and earth floating on an infinite ocean ● Anaximander ○ Apeiron: “infinite” ○ Suggested that all material things arose from and returned to the apeiron ■ Allowed him to imagine that worlds might be born and die repeatedly through eternal time ● Consensus emerged in favor of world being built from 4 elements 1. Fire 2. Water 3. Earth 4. Air ● Two different schools of thought formed concerning the nature and extent of these elements 1. Atomists: both Earth and Heaven were made from an infinite number of indivisible atoms of each of the four elements 2. Aristotelians: four elements- not necessarily made from atoms- were confined to the realm of Earth while 5th element called “aether” (or ehter) or the “quintessence” (fifth element) ● Atomists ○ Developed by DEMOCRITUS argued that world (e+h) had been created by the random motions of infinite atoms ○ Because atoms were infinite it was natural to assume that the same processes that created our world could also have created others ○ “There are infinite worlds both like and unlike this world of ours, we must believe that in all worlds there are living creatures and plants and the other things we see in this world” ● Aristotelians ○ ARISTOTLE: believed that each of the four elements had its own natural motion and place ■ Eg. earth moved naturally toward the center of the universe ■ Eg. fire naturally rose away from center and up to sky ○ If there was more than one world, there would be more than one natural place for the elements to go which is illogical ○ “The world must be unique...there cannot be several worlds” ● Debate about extraterrestrial eventually became intertwined with religion and became messy //COPERNICAN REVOLUTION ● Copernicus published (Revolutions of the Heavenly Spheres) launching the copernican revolution ○ Revived Aristarchus’s radical sun centered idea and described it with enough mathematical proof to make it a legit competitor for the Ptolemaic Model ○ Scientists who debated this idea formed the foundation for modern science //Copernicus ● Adopted Aristarchus’ sun centered idea probably because he was drawn to the simplicity ● C discovered simple geometric relationships that allowed him to calculate each planet’s orbital period around the sun and relative distance from the sun ● Success of his model in proving a geometric layout for the solar system further convinced him that the sun-centered idea must be correct ● (-) still held the ancient belief that heavenly motion must occur in perfect circles which added numerous complexities to his model //Tycho ● Hard for astronomers at the time to improve because they lacked quality data due to telescope not being invented yet ● Tycho came along and built large naked eye observatories which made data much more reliable //Kepler ● Believed planetary orbits should be perfect circles and eventually found a set of circular orbits that matched tycho’s observations (8 min apart) ● Wasn’t happy with discrepancies and they caused him to abandon the idea of circular orbits ○ This decision to trust data over beliefs was a huge turning point ● CORRECT: stated that planetary orbits take shapes of special types of ovals called orbits Kepler’s Laws of planetary motion ● Kepler’s first law: the orbit of each planet about the sun is an ellipse with the sun at one focus ○ Basically states that planet’s distance from the sun varies during its orbit ○ Perihelion: (near the sun) closest point of orbit to the sun ○ Aphelion (away from the sun) point farthest away from sun ○ Semi Major axis: average distance from sun