Cosmology and the Birth of Earth Where do we come from Where do we fit in the Universe Why are we here Cosmology Study of the structure and evolution of the universe Cosmology is a complicated science Requires thinking in unfamiliar scales of space and time Spatial Scales Attometers 10 21 meters to 10s of billions of light years 9 4622 meters Temporal scales attoseconds 10 21 seconds to 10s of billions of years 3 1517 seconds Earth changing place 3 000 years ago humans knew the heavens well Stars were fixed relative to other stars Stars moved predictably across the sky They saw retrograde motion separating planets from stars They did not think of Earth as a planet however Movement in the heavens was attributed to deities An evolving image of Earth The ancients thought the universe was geocentric Heavenly bodies circle around a motionless central geocentric Proven by Ptolemy the idea was still wrong Yet it held as doctrine for 1 400 years during the dark ages It became religious dogma supporting the importance of Earth in the Scheme of heaven The Renaissance A rebirth of rational thinking in 15th century Europe Galileo observed moons orbiting Jupiter Copernicus published evidence for heliocentricity Kepler his elliptical planetary orbits refuted Ptolemy Heliocentric ideas Earth didn t center the universe Planetary orbits weren t circular Not all bodies orbited earth Planes including earth orbit the sun The enlightenment Sir Isaac Newton devised The law of universal gravitation The three laws of motion The mathematics of change calculus He proved that natural law governs natural events Geocentricity faded away Earth as a sphere A flat was dispelled by 250 BCE Abundant evidence suggested a spherical earth A curved shadow crossed the moon during eclipses Only the tops of distant sailings ships were visible In 1520 Magellan circumnavigated this sphere A flat earth will receive light at a right angle at noon everywhere during summer solstice A round Earth will receive light at diminishing angles toward the poles at noon during summer solstice Eratosthenes measured Earth to be 252 000 Egyptian Stadia or 39 630km in circumference 1 error Earth Rotation How do we know that Earth Rotates Clearly visible in a time lapse photograph of the night sky Foucault s pendulum 1851 proved Earth s rotation Distance from Earth We must consider huge expanses of space and time The speed of light is 186 000 miles s 300 000 km s The moon is 1 3 light seconds 237 00 miles away The sun is 8 3 light minutes 93 million miles away A light year measures a distance of 5 87 trillion miles Alpha Centauri the closest star is 4 3 light years away The visible universe is 13 billion light years away Modern view of the Universe Current concepts differ wildly from 100 years ago Earth is one of eight planets in the solar system The solar system is on an arm of the milky way galaxy Our Sun is one of 300 billion stars in this galaxy The Doppler effect Waves compress or relax with relative motion Applies to waves of both sound and light The stopped train sounds the same to Anna and Bill Anna hears a higher pitch from compressed sound waves Bill hears a lower pitch from expanded sound waves As the train passed Anna the pitch would drop higher to lower This is commonly heard as cars whiz on a road Light waves behave like sound waves Visible light is electromagnetic radiation Visible wavelengths range from 400 to 700 nanometers 400 nm blue higher frequency 700 nm red lower frequency A moving star displays Doppler shifted light Light from an approaching star is compressed This causes a shift to higher frequencies so that Stars moving toward Earth are shifted toward blue Light from a receding star is expanded This causes a shift to lower frequencies so that Stars moving away from Earth are shifted toward red The Expanding Universe Light from distant galaxies appeared red shifted In 1929 Hubble recognized this as a Doppler shift He concluded that galaxies were moving away rapidly No galaxies were found to be moving toward Earth This led to the development of the expanding Universe Theory analogous to expanding bread Origin of the Universe The Big Bang Theory When did the expanding Universe begin The best answer so far The big bang All of the mass and energy in the Universe was packed into a single small point It exploded 13 7 Ga and has been expanding eve since The 1st atoms hydrogen and helium of the universe developed soon after the big bang These atoms formed vast gas clouds called nebulae Evidence Expansion of the Universe Hubble s Law Other evidence for the Big Bang Universe Composition Edwin Hubble discovered that distant galaxies are uniformly red shifted rather than blue shifted galaxies are moving AWAY from us Started out 100 Hydrogen and Helium Nucleosynthesis occurred only during earliest stages of the Big Bang Explains present composition 90 H 10 He 1 heavier elements After the Big Bang With expansion and cooling atoms began to bond Hydrogen formed H2 molecules the fuel of stars Atoms and molecules coalesced into gaseous nebulae Gravity caused collapse of gaseous nebulae Collapse resulted in increases in Temperature Density Rate of rotation After the Big Bang Condense nebulae formed flattened accretion discs Heat and mass from collapse ignited nuclear fusion These 1st generation stars consumed H2 fuel rapidly As the stars became H2 starved they initiated Collapse and heating Heavy element production Catastrophic explosion supernova Nucleosynthesis Stars are truly element factories Big Bang nucleosynthesis formed lighter elements Heavier elements are from stellar nucleosynthesis Elements with atomic s 26 form during supernovae The mass of a star governs its element production Smaller mass stars like the Sun Burn slowly Live loner 10 Ga Create lighter elements up to carbon c Larger mass star 10 100x the mass of the sun Burn rapidly Are shorter lived 10s of Ma Create heavier elements up to iron Fe When fuel dwindles stars heat by inward collapse This leads to a cataclysmic explosion a supernova The supernova creates heavier elements The Solar System Earth shares the solar system with 7 other planets Planet A precise definition developed in 2006 A planet 4 Is a large solid body orbiting a star e g the Sun 4 Has a nearly spherical shape 4H as cleared its neighborhood of other objects 4Thus Pluto previously defined as a planet is excluded now belonging to the Kuiper Belt Moon A solid body locked in orbit around a planet
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