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Topic 3 Earth in the Universe Rotation vs. Revolution Rotation: an object spinning on its axis Revolution: an object orbiting around another object or point in space A Survey of the Solar System Geocentric vs. Heliocentric Improving the heliocentric model • Galileo saw Venus experience phases like the Moon and saw satellites orbiting Jupiter Isaac Newton’s Law of Universal Gravitation The force of attraction between two objects is greater with increased masses of the objects and less with increased distance between them. Kepler’s Laws of Planetary Motion 1. The orbital paths of the planets are elliptical, with the Sun at one focus SHAPE OF ELLIPSES Eccentricity = 0 circle Eccentricity = 0.5 Eccentricity = 1 line • TO THE HUMAN EYE, MOST ORBITS OF PLANETS LOOK LIKE CIRCLES • SLIGHTLY ELLIPTICAL SHAPE OF EARTH’S ORBIT CAUSES THE PLANET TO VARY THE DISTANCE TO THE SUN DURING REVOLUTION 147 million kms. 152 million kms. Gravitational Effects of Varying the Distance to the Sun Gravitation force influenced by mass and distance 1. Greater the mass = greater the gravitational attraction 2. Closer the 2 objects = greater the gravitational attraction Perihelion = greater gravitational attraction Aphelion = less gravitational attraction Mass stays the same but distance varies causing gravitational attraction to vary If gravitational attraction varies, velocity will vary Perihelion = faster velocity Aphelion = slower velocity Appearance of Sun Changes with Varying Distance Terrestrial Observations that support the Heliocentric Model 1. Foucault Pendulum 1. Evidence of Earth’s Rotation • 1851, Foucault’s pendulum will appear to change in a predictable way. • Why is this evidence? There is no force acting on the pendulum to make its plane of oscillation rotate or go around its own axis • It would continue to swing in the original path if Earth did not rotate. No force that makes pendulum rotate – must be earth that is rotating!!! 2. Evidence for Rotation • Coriolis Effect – the tendency of objects moving over the earth (air, water, planes, projectiles) to be deflected (curve away) from a straight line path. The French scientist, Gaspard Coriolis, first explained the deflection of objects moving over the surface due to Earth’s rotation • The deflection is to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. • This deflection occurs because Earth’s surface is rotating with respect to the objects. Planetary Orbits and Rotation Tipped over by more than 900 Mercury and Pluto: Unusually highly inclined orbits Two Kinds of Planets Planets of our solar system can be divided into two very different kinds: Terrestrial (earthlike) planets: Mercury, Venus, Earth, Mars Jovian (Jupiter-like) planets: Jupiter, Saturn, Uranus, Neptune Size of Terrestrial Planets Compared to Jovian Planets Terrestrial Planets Four inner planets of the solar system Relatively small in size and mass (Earth is the largest and most massive) Rocky surface Surface of Venus can not be seen directly from Earth because of its dense cloud cover. The Jovian Planets Much larger in mass and size than terrestrial planets Much lower average density All have rings (not only Saturn!) Mostly gas; no solid surface Space Debris In addition to planets, small bodies orbit the sun: Asteroids, comets, meteoroids Asteroid Eros, imaged by the NEAR spacecraft The Asteroid Belt Most asteroids orbit the sun in a wide zone between the orbits of Mars and Jupiter. (Distances and times reproduced to scale) Comets Icy nucleus, which evaporates and gets blown into space by solar wind pressure. Mostly objects in highly elliptical orbits, occasionally coming close to the sun. The tail of a comet always points away from the Sun. Meteoroids Small (mm – mm sized) dust grains throughout the solar system If they collide with Earth, they evaporate in the atmosphere. Visible as streaks of light (“shooting stars”): meteors. THE SOLAR SYSTEM HELIOCENTRIC 100,000 light- years less than 0.01 light years THE UNIVERSE THE GALAXY THE SOLAR SYSTEM THE PLANET Going beyond our solar system…… The stars appear to rise and set because the Earth rotates beneath them The complete circular path can be seen for stars in the northern part of the sky around Polaris Circumpolar constellations never set. Circumpolar constellations change with latitude… sky changes with latitude Brightness of Stars Absolute magnitude/luminosity: the actual amount of light given off by a star Apparent magnitude: the amount of light given off by a star AS SEEN FROM EARTH . Light year: the distance light travels in one year = 9.5 trillion km (light travels 300,000 km/sec) Star Life Cycle: Stars are like humans. They are born, live and then die. • Nebula – cloud of gas and dust Protostar – new, just forming star Stars start from clouds Clouds provide the gas and dust from which stars form. But not this kind of dust Rather: Irregular Grains Of Carbon or Silicon At 15 million degrees Celsius in the center of the star - nuclear fusion begins Star Formation Stars exist because of gravity Two opposing forces in a star are • Gravity – contracts • Nuclear fusion – expands A Balancing Act Energy released from nuclear fusion counteracts inward force of gravity. Throughout its life, these two forces determine the stages of a star’s life. Star’s Life Cycles Hertzsprung-Russell Diagram aka Luminosity and Temperature of Stars Diagram – NOT A MAP DIAGRAM IS A USEFUL WAY TO FOLLOW CHANGES THAT TAKE PLACE AS THE STARS LIVE OUT THEIR LIVES Diagram is made by plotting (graphing) each star's LUMINOSITY (brightness) and TEMPERATURE (as reflected by color) COMPARED TO THE SUN Most stars are on the Main Sequence because that is where they spend most of their lives Our sun is an average main sequence star Luminosity of 1 Temperature 5500°C – yellow in color Classifying Stars based on luminosity and temperature Schematically, stars fall into regions shown below with respect to the sun. All planets compared to Our Sun No longer considered a planet Hertzsprung-Russell Diagram Star Evolution • Giants (or red giants) • Very luminous (These stars are enormously bright for their temperature due to their size (10x size of sun) • Low Temperature • Represent the late evolution of medium-sized main sequence stars when they greatly expand in size Hertzsprung-Russell Diagram Star Evolution • Super Giants (100 to 1,000 times diameter of sun) • Only a few percent of all stars • They represent the late evolution of stars more massive than the sun. • Usually explode in a supernova event H-R Diagram – Star Evolution White dwarfs •Small (approximate the size of Earth) •Hot •Low in luminosity (due to their small size) Black dwarfs – dead stars THE SOLAR SYSTEM HELIOCENTRIC 100,000 light- years less than 0.01 light years THE UNIVERSE THE GALAXY THE SOLAR SYSTEM THE PLANET THE GALAXY • The Milky Way Galaxy – Over 100 billion stars in our galaxy – The Sun = 1 of those stars THE SUN (Our Solar System) 100,000 light years Speed of Light = 670,616,700 mph UNIVERSE = THE BEACH GALAXY = GRAIN OF SAND THE UNIVERSE THE GALAXY THE SOLAR SYSTEM THE PLANET The structure of the Universe A galaxy is a collection of billions of stars held together by gravity The universe contains billions of galaxies and each galaxy contains billions of stars. Our galaxy is a spiral galaxy called the Milky Way CLUSTERS OF GALAXIES • Many times galaxies are seen in clusters • Our Galaxy is found in a cluster GALAXY THE UNIVERSE THE GALAXY THE SOLAR SYSTEM THE PLANET THE UNIVERSE • The Universe – everything that physically exists – contains billions of galaxies Clusters of Galaxies THE UNIVERSE THE GALAXY THE SOLAR SYSTEM THE PLANET Big Bang theory – Origin of the Universe Big Bang marks the inception of the universe • Occurred about 15 billion years ago • All matter and space was created Not a huge explosion that hurled matter in all directions. Technically, there was no “bang” Technically, matter is not moving outward in all directions. Reality: space expands Origin of the Universe Big Bang Evidence • More distant galaxy – moving WITH space as space itself expands • Think loaf of unbaked raisin bread. The raisins are galaxies and the dough is space Raisin bread analogy of an expanding universe Expansion Evidence Stars are made of elemental gases that emit specific wavelengths within the electromagnetic spectrum based on their chemical composition. Each gas emits certain wavelengths that are unique to that element. The combination of a star’s elements which produce a pattern of spectral lines can be used to identify the star rather like a fingerprint or bar code. Spectral lines are lines that correspond to various wavelengths seen in an element’s spectrum. Red Shift – Blue Shift In 1929, Edwin Hubble observed that spectral lines emitted by stars in distant galaxies were considerably Red shifted. The spectral lines (fingerprint or bar code) of stars coming towards Earth were shifted to the blue light end of the spectrum (shorter wavelength) The spectral lines (fingerprint or bar code) of stars going away from Earth were shifted to red light end of the spectrum (longer wavelength) Shifting of Wavelengths is called the Doppler Effect • Change in the wavelength of light emitted by an object due to its motion • Movement toward “squeezes” the wavelength • Shorter wavelength • Light shifted toward the blue end of the spectrum • Movement away stretches the wavelength • Longer wavelength • Light shifted toward the red end of spectrum RED SHIFT – BLUE SHIFT • The greater the degree of shift of the spectral lines, the faster the object is moving away • The star light DOES NOT appear red or blue (it still appears as white light from the star) • The “bar code” for each element either shifts to the shorter wavelength blue end of the spectrum or to the longer wavelength red end of the spectrum What is the best inference that can be made concerning the movements of Galaxies A, B, and C? Other Evidence for Big Bang • Energy created by big bang expanded along with matter • Should be radiation all over the universe mixed in with energy given off by stars • Evidence of long wavelength background radiation (actually microwaves) appear to be coming from all directions in the universe • Background radiation was discovered in 1964 by Arno Penzias and Robert Wilson, who later won the Nobel Prize for this discovery