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by: Mrs. Edison Conn

ExplorationoftheUniverse ASTR105

Marketplace > Eastern Michigan University > Astronomy > ASTR105 > ExplorationoftheUniverse
Mrs. Edison Conn
GPA 3.65


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Class Notes
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This 23 page Class Notes was uploaded by Mrs. Edison Conn on Sunday October 11, 2015. The Class Notes belongs to ASTR105 at Eastern Michigan University taught by PatrickKoehn in Fall. Since its upload, it has received 31 views. For similar materials see /class/221474/astr105-eastern-michigan-university in Astronomy at Eastern Michigan University.


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Date Created: 10/11/15
Chapter 1 History of Astronomy CopyvgmcThe Msevaw Hll Companies lm Pevmsson equvedtovveDvodwtonovdleay Periods of Western Astronomy Western astronomy divides into 4 periods 7 Prehistoric before 500 BC 0 Cyclical motions of Sun Moon and stars observed 0 Keeping time and determining directions develops 7 Classical 500 BC to AD 1400 0 Measurements of the heavens 0 Geometry and models to explain motions 7 Renaissance 1400 to 1650 o Accumulation of data led to better models 0 Technology the telescope enters picture 7 Modern 1650 to present 0 Physical laws and mathematical techniques 0 Technological advances accelerate The heavens have been Prehistoric Astronomy Cuwrumemu mew uuiconuaym Permigm mqu in Numuahunarmwlw studied for thousands of years Early astronomers noted the obvious 7 Rising of the Sun in the eastern sky and its setting in the west 7 Changing appearance of the Moon 7 Eclipses 7 Planets as a distinct class of objects different from the stars Prehistoric Astronomy Many astronomical phenomena are cyclic on a day to day and year to year basis and consequently gave prehistoricrpeople Newt 11 Methods for keepih f5 Ability to predict and plan future events Incentive to build monumental structures such as Stonehenge 39 r Modern civilization no longer relies on direct astronomical observations for time keeping and planning To C iur mnet Sunrise Studying the night sky provides link to past Stonehenge Copying a The Celestial Sphere Vast distances to stars prevent us from sensing their true 3D arrangement Naked eye observations treat all stars at the same distance on a giant celestial sphere with the Earth at its center Models and Science 0 The celestial Sphere W we m mmmmmmmmmmmmmmmmmmmm W is a model which quot Stars reoll 39 oulllierey Stars really oullhere necessarily match gg phys1cal reality 0 Models provide a means to enhance our understanding Horizon of nature Our Experience of the Celestial Sphere Constellations Copyright 6 The McGrawHIll Companies Inc Permissxm required In reproduullun or display Constellations are fixed arrangements of stars that resemble animals objects and mythological figures 0 Stars in a constellation are not physically related Constellations Copyright The McGrawHlll Companies Inc Purmlssuan requived or reproduclion or display Positions of stars change very Origin of the ancient slowly constellations W111 constellations is unknown look the same for thousands although they probably SCFVed of years as mnemonic tools for tracking seasons and navigation Diurnal Vs Annular Motion Diurnal Motion Annual Motion Daily MOtiOH Yearly Motion Sunz M0011 planetsa Due to the Earth s and stars rise in the revolution east and set in the west 31338516 Earth S Is the sky different from day to day Month to month Ancient astronomers took all celestial motion to be diurnal The Celestial Sphere Year to year Diurnal Motion 0 Daily motion can be explained by the rotation f 39 i of the celestial sphere about the north and south celestial poles located directly above the Earth s north and south poles The celestial equator which lies directly above the Earth s equator provides another 5 39 Ce39e e astronomical reference marker South Noth celesnu North Annual Motion Cam glut The Meanlull Emupanms trc Pmrmssnn mquued lm lepmducl m m L l iif E cram 39v hing August Fwdxgln lookan westward June I Nillgl ll baiting wcslword jemim For a given time say 1000 PM as the months proceed constellations do not appear in the same part of the sky Annual Motion 0 A given star rises 3 minutes 56 seconds earlier each night 0 This annual motion is caused by the Earth s 17 motion around the Sun the result of projection The ancients used the periodic annual motion to mark the seasons The Ecliptic 0 The path of the Sun through the stars on the celestial sphere is I V called the ecliptic virg x N The ecliptic is a I l 1 i quotS October V g pI O ection of the 9 quot Earth s orbit onto the Ecliptic gtputh celestial sphere and is tipped relative to the celestial equator The Seasons Copyright The MuGrawHlll Companies Inc Permlssion ruqulred tor reproduction or display Noth Pole 1 l l l 1 2 a a Q ToSun 2339s Equator The Earth is closest to the Sun in January which is winter in the northern hemisphere A 0 Therefore the seasons cannot be caused by the Sun s proximity to the Earth 0 The Earth s rotation axis is tilted 235 from a line perpendicular to the Earth s orbital plane The Seasons Septem ber The rotation axis of the Earth maintains nearly the same tilt and direction from year to year The northern and southern hemispheres alternate receiving on a yearly cycle the majority of direct light from the Sun This leads to the seasons The Seasons Copyright The McGrawHill Companies Inc Permission required for reproduction or display North Pole 5911010 i r 3 7 Sunlight Winier Less heat is received because the surface is quottiltedquot Seasons and The Ecliptic The tilt of the Earth s rotation axis causes the ecliptic not to be aligned with the celestial equator Sun is above celestial equator in June when the Northern Hemisphere is tipped toward the Sun and is below the equator in December when tipped away Tilting explains seasonal altitude of Sun at noon highest in summer and lowest in winter The Ecliptic s Tilt Copyright The McGraw Hill Companies Inc Permission required for reproduction or display Earth s position in its orbit Sun39s position on celestial at different times of year sphere of start of each season North celestial pole Sun on June 21 torihest North Cell Eq quot f North pole O h quot t i quot 7 Eclip Sun on March 2 on 5 q C l eeshq Equmor Q Norih pole fie Sun Solstices and Equinoxes Points on horizon where Sunrises and sets changes periodically throughout year 0 In summer months of Northern hemisphere the Sun rises north of east and sets north of west 0 In winter months of Northern hemisphere the Sun rises south of east and sets south of west 0 The solstices about June 21 and December 21 are when the Sun rises at the most extreme north and south points 0 The equinoxes equal day ancinight and about March 21 and September 23 arewhen the Sun rises directly east Ancients marked position of Sun rising and setting to determine the seasons e g Stonehenge V Solstices and Equinoxes CDWDQDI til June March September December Sunnnersobhcel Equinoxes VVh ersob ce South Planets and the Zodiac Copyright 9 The Inc 1 repxuuu mm or display The planets Greek for wanderers do not follow the same cyclic behavior of the stars The planets move relative to the stars in a very narrow band centered about the Motion and location of the planets in the sky is a combination of all the planets orbits being nearly in the same plane and their relative speeds about the Sun ecliptic and called the zodiac Planets and the Zodiac Apparent motion of planets is usually from west to east relative to the stars although on a daily basis the planets always rise in the east Copyright The McGrawHiil Companies Inc Permission required for reproduction or display celes ol pole Eclipric The Earth s orbital plane Zod39roc celes al equator Copyngm o Declination Degrees N 39 July 12 1995 i2 ll Retrograde Motion 1 Morch 25 1995 o n Sepl 30 1992 x39 Ocr 25 I 994 10 B 7 b 9 Right Ascension Hours 39 Occasionally a planet will move from east to west relative to the stars this is called retrograde motion Explaining retrograde motion was one of the main reasons astronomers ultimately rejected the idea of the Earth being located at the center of the solar system The Moon Rises in the east and sets in the west Like the planets and Sun the Moon moves from west to east relative to the stars roughly the width of the Moon in J one hour The Phases of the Moon 0 During a period of about 30 days the Moon goes through a complete set of phases new waxing crescent first quarter waXing gibbous full waning gibbous third quarter waning crescent The Phases of the Moon Sunlight quotVI The phase cycle is the origin of the month derived from the word moon as a time period The phases of the Moon are caused by the relative positions of the Sun Earth and Moon Lunar Rise and Set Times 0 The Moon rises roughly 50 minutes later each day Firsl quarter af w d D Jr 11 X To Sun a i i Evening quot 39 39L 39l I Iquot W m zz Third quarter Eclipses Copyright The McGraw Hill Companies Inc Permission required for reproduction or display Moon s shadow touches Earihl What you see from Earth An eclipse occurs when the Sun Earth and Moon are directly in line with each other A solar eclipse occurs when the Moon passes between the Sun and Earth with the Moon casting its shadow on the Earth causing a midday sky to become dark as night for a few minutes Solar Eclipse from Space Cop rugquot 6 im ermi lO Lunar Eclipses Copyright The McGraw Hill Companies inc Permission required for reproduction or display K What you see from Earth A lunar eclipse occurs when the Earth passes between the Sun and Moon with the Earth casting its shadow on the Moon giving it a dull red color Eclipse Periods Copyrigth c Im 39 Moon s orbit M Plane of Earih s orbit The Ecliptic l Eurih39s shadow Moon Moon39s shadow Eclipses do not occur every 30 days since the Moon s orbit is tipped relative to the Earth s orbit The tipped orbit allows the shadow of the Earth Moon to miss the Moon Earth Moon s shadow Ancient Greek Astronomers Through the use of models and observations they were the first to use a careful and systematic manner to explain the workings of the heavens Limited to nakedeye observations their idea of using logic and mathematics as tools for investigating nature is still with us today 0 Their investigative methodology is in many ways as important as the discoveries themselves ll Early Ideas Pythagoras Pythagoras taught as early as 500 BC that the Earth was round based on the belief that the sphere is the perfect shape used by the gods Early Ideas Aristotle w I r M amw mxcmmu m mmmnmmtuvummnanmmpny By 300 BC Aristotle presented naked eye E r39h h d w observations for the Earth s spherical shape Shape of Earth s shadow on the Moon during an eclipse 5 a He also noted that a traveler moving south will see stars previously hidden by the southern horizon 12 Early Ideas The Size of the Earth 5 m Parmmsmv mqmmd by quotWWW Eratosthenes 276 195 BC made the first measurement of the Earth s size He obtained a value of 25000 miles for the circumference a value very close to today s value display Early Ideas The Size of the Earth He measured the shadow length of a stick set vertically in the ground in the town of Alexandria on the summer solstice at noon converting the shadow length to an angle of solar light incidence and using the distance to Syene quot wensvens a town where no shadow is cast at noon on the summer solstice The sizes and Early Ideas Distance and Size of the Sun and Moon mwum r wan Earth were determined by Aristarchus about 75 years before Eratosthenes measured the Earth s size Once the actual size of the Earth was determined the absolute sizes and distances of the Sun and Moon could be determined distances of the Sun M9 39 and Moon relative to oFMbon giggly ttttt m l3 Early Ideas Distance and Size of the Sun and Moon Enwugmb w mew mu swarm rra Pamts These relative sizes were based on the angular size of objects and a simple geometry formula relating the object s diameter its angular size and its distance Early Ideas Distance and Size of the Sun and Moon samrwm na Malauw um L mvvamlus I parquoter mum Am rummrarr m m Earth in January Star m he 1 l r Sun 3 j quot rrua position I r r r appears rs in July at nearby slur Star appears here in January quot1 Euth in luly Aristarchus realizing the Sun was very large proposed the Sun as center of the Solar System but the lack of parallax argued against such a model Early Ideas Thequot GeOcentric Model l Because of the general ealst to west motion on objects in the sky geocentric theories were developed to explain the motions 39 Eudoxus 400 347 BC proposed a geocentric model in which each celestial object was mounted on its own revolving transparent sphere with its own separate tilt The faster an object moved in the sky the smaller was its corresponding sphere This simple geocentric model could not explain retrograde motion without appealing to clumsy and unappealing contrivances Early Ideas The Geocentric Model Moon Earth Venus Sun Mars Jupiter Ptolemy of Alexandria Ptolemy of Alexandria improved the geocentric model by assuming each planet moved on a small circle which in turn had its center move on a much larger circle centered on the Earth The small circles were called epicycles and were incorporated so as to explain retrograde motion Epicycle Plane Ptolemy of Alexandria Ptolemy s model was able to predict planetary motion with fair precision Discrepancies remained and this led to the development of very complex Ptolemaic models up until about the 1500s Ultimately all the geocentric models collapsed under the weight of Occam s razor and the heliocentric models prevailed 15 Non Western Contributions Islamic Contributions Relied on celestial phenomena to set its religious calendar Created a large vocabulary still evident today eg zenith Betelgeuse Developed algebra and Arabic numerals Asian Contributions Devised constellations based on Asian mythologies Kept detailed records of unusual celestial events eg eclipses comets supernova and sunspots Eclipse predictions Astronomy in the Renaissance man o u may Nicolaus Copernicus 147 31543 Could not reconcile centuries of data with Ptolemy s geocentric model Consequently Copernicus reconsidered Aristarchus s heliocentric model with the Sun at the center of the solar system Heliocentric models Astronomy in the Renaissance oowwmem mew mucomrm lm F vnummn mqu tor mpmdmhunurmsplav N explain retrograde motion as a natural consequence of two planets one being the Earth passing each other Copernicus could also derive the relative distances of the planets from the Sun l6 Astronomy in the Renaissance Cuwulgm a 0 However problems remained Could not predict planet positions any more accurately than the model of Ptolemy Could not explain lack of parallax motion of stars Conflicted with Aristotelian common sense Astronomy in the Renaissance uuuuuuuuuuuuuuuuuuuuuuu 0mm w Mm mun tampmmmwwm Tycho Brahe 1546 1601 Designed and built instruments of far greater accuracy than any yet devised Made meticulous measurements of the planets Tycho Brahe 15461601 Made observations supernova and comet that suggested that the heavens were both changeable and more complex than previously believed Proposed compromise geocentric model as he observed no parallax motion l7 Astronomy in Johannes Kepler 1571 l 63 0 Upon Tycho s death his data passed to Kepler his young assistant Using the very precise Mars data Kepler showed the orbit to be an ellipse the Re Planets move in elliptical orbits With the Sun at one focus of the ellipse Tacks cl each rows or Ellipse The orbital speed of a planet varies so that a line joining the Sun sweep out equal areas in equal time intervals and the planet will Q The Closer a planet is to the Sun the faster it moves ay 2 months 39 For example 2 months for example 18 Kepler s The amount of time a planet takes to orbit the Sun is related to its orbit s size The square of the period P is proportional to the cube of the semimajor axis a 3rd Law camwmem Mnenw mimomnws m w mm mqu m Mpmduulmnmdiiptw P2 years 03 AU P time to complete orbit a semimajor axis C Kepler s 3rd Law This law implies that a planet with a larger average distance from the Sun which is the semimaj or axis distance will take longer to circle the Sun Third law hints at the nature of the force holding the planets in orbit CownymmleMneww mucomms m Farminan mquimd luv ripmdmncnmmiplav P2 years 03 AU P time to complete orbit a semimajor axis C Kepler s Third law can be used to determine the semimajor axis a if the period P is known a measurement that is not dif cult to make 3rd Law CownymmleMneww mucomms m Farminan mquimd luv ripmdmncnmmiplav P2 years 03 AU P time to complete orbit a semimajor axis C l9 Astronomy in the Renaissance new Galileo 1564 1642 Contemporary of Kepler First person to use the telescope to study the heavens and offer interpretations The Moon s surface has features similar to that of the Earth 3 The Moon is a ball of rock Astronomy in the Renaissance The Sun has spots 3 The Sun is not perfect changes its appearance and rotates Jupiter has four objects orbiting it 3 The objects are moons and they are not circling Earth Milky Way is populated by uncountable number of stars 3 Earth centered universe is too simple Evidence for the Heliocentric Model cowgw e m M aw mu mum s h ammm matured 1m tunrvjmmn or may Venus k Gibbons phase Venus undergoes full phase cycle gt Venus must circle Sun 20 Astronomy in the Renaissance Credited with originating the experimental method for studying scienti c problems Deduced the first correct laws of motion Was brought before the Inquisition and put under house arrest for the remainder of his life Isaac Newton 1642 1727 was born the year Galileo died He made major advances in mathematics physics and astronomy Isaac Newton 0 He pioneered the modern studies of motion optics and gravity and discovered the mathematical methods of calculus It was not until the 20 h century that Newton s laws of motion and gravity were modified by the theories of relativity 21 The Growth of Astrophysics 39 New Discoveries 7 In 1781 Sir William Herschel discovered Uranus he also discovered that stars can have companions 7 lrregularities in Uranus s orbit together with law of gravity led to discovery of Neptune 39 New Technologies 7 Improved optics led to bigger telescopes and the discovery of nebulas and galaxies 7 Photography allowed the detection of very faint objects The Growth of Astrophysics 39 The Nature of Matter and Heat 7 The ancient Greeks introduced the idea of the atom Greek for uncuttable which today has been modified to include a nucleus and a surrounding cloud of electrons 7 Heating transfer of energy and the motion of atoms was an important topic in the 1700s and 1800s The Growth of Astrophysics 39 The Kelvin Temperature Scale 7 An object s temperature is directly related to its energy content and to the speed of molecular motion 7 As a body is cooled to zero Kelvin molecular motion within it slows to a virtual halt and its energy approaches zero 3 no negative temperatures 7 Fahrenheit and Celsius are two other temperature scales that are easily converted to Kelvin 22 The Kelvin Temperature Scale Copyright The McGrawHill Companies Inc Permission required for reproduction or display 15000000K 15oooooo gtc 2700000ch Sun score 5800K 5526 C 9980 F Sun s surface 2000K i727 C 3 1 40 F Lighi bulb filament Wafer boils Human body Room temperoiure Water freezes Dry ice Liquid nitrogen Absolute zero 23


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