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Astronomy 180 AST-180 (John F Astronomy 180 AST-180 (John F. Wettaw College of Biological Sciences) 8/28/08 Astronomy – The study of the Universe. Universe – All objects in it, its properties, and its evolution. Pseudoscience – Seems like a science, but is not actually a science. Astronomy is the earliest /oldest science. Reasons for studying Astronomy: Fun Religious Navigation Calendar Curiosity Astrology Mythology Disaster Warning/Prevention Resources/Expansion Aid to other sciences Tides Scientific Method 1. Make an observation. 2. Make a model (hypothesis). Explain observation Predict future results 3. Test model in a variety of situations. 4. Theory (-> Law potentially) 9/2/08 Patterns of Stars – Constellations (Currently accepted constellations are from the Greeks). They can represent objects, animals, or mythological beings. International Astronomical Union (IAU) – Subdivided the sky info 88 constellations. Angular Measurement – 360 Degrees in a circle, 60 arcminutes in a degree, 60 arcseconds in an arcminute. The full moon or sun are about 0.5 degrees. Distances in Astronomy: Within Solar System: Astronomical Unit (Au) – Average distance between the Earth and the Sun. 1 Au = 93m miles = 9.3 x 107 mi = 1.5 x 108 km Outside Solar System: Light year – Distance light can travel in one year. 1 LY = 6 x 1012 mi = 1013 km Parsec – A larger unit of distance. 1 Pa = 3.09 x 1013 = 3.26 LY Electromagnetic Radiation Visible Light Radio Waves X-Rays 9/4/08 Asterisms – Prominent groupings of stars not officially recognized as constellations by the IAU. For instance: The Big/Little Dipper, or The Summer Triangle Celestial Sphere – Sphere around earth for computing a stars position. Polaris – The North Star. Circum Polar Stars – Starts that never rise or set. Ecliptic – The Suns path across the Celestial Sphere. Zodiac Constellations – Constellations through which the Sun passes. Declination – The Celestial Sphere’s equivalent of Latitude (N/S). N/S of Celestial Equator. Right Ascension – The Celestial Sphere’s equivalent of Longitude (E/W) 0 RA = The Vernal Equinox Only measured toward the east. Measured in time units (H/M/S). Revolution – The orbital motion of one body around another. Rotation – The spin motion of a body. Coordinate System (Earth) Latitude (N-S) 0° Lat = Equator +90° Lat = North Pole -90° Lat = South Pole Longitude (E-W) 180° W - 180° E 0° Long = Prime Meridian (Greenwich England) 1 Rotation of the earth = 1 day 1 Revolution of the moon around the earth = 1 month 1 Revolution of the earth around the sun = 1 year 9/9/08 Noon-noon – Solar Day, 24hrs. Sidereal Day – Time for stars to return to the same position, 23h 56m 4s. Perihelion – Closest point to the Sun. Aphelion – Farthest point from the Sun. Season – Tilt of rotational axis. Precession – Wobbling of Earth’s rotation axis. Sidereal Month – Time to return to the same background of stars (27 1/3 earth days long). Synodic Month – Time to return to the same phase (29 ½ earth days long). The Earth’s orbital motion around the sun accounts for 4min difference. 1 Orbit (Revolution) of the Earth around the Sun is 1 Year (365.2425 days). 1 Revolution of the Moon around the Earth is 1 Month. Earth’s Orbit around the Sun Perihelion = 1.47 x 108 – January 4th. Aphelion = 1.52 x 108 – July 4th. Sun/Stars create their own energy. Planets/Moons reflect light. Phases of the Moon as viewed from above the north pole. Phases of the Moon as viewed from the earth. Autumnal Equinox – Sept 21st. Sun overhead at noon at the equator. Equal number of day and night hours. Vernal Equinox – Mar 21st. Sun overhead at noon at equator. Equal number of day and night hours. Summer Solstice – Jun 21st. Sun overhead at noon at 23.5° N Latitude. Max number of daylight hours. Winter Solstice – Dec 21st. Sun overhead at noon at 23.5° S Latitude. Max number of nighttime hours. 9/11/08 Perigee – Moon’s closest approach to Earth. Apogee – When the Moon is farthest from Earth. Eclipses Solar Eclipse – Moon blocks out light from sun as seen from Earth. New Moon phase only. Total Solar Eclipse – Occurs when the Moon completely blocks out the sun. Annular Solar Eclipse – Occurs when the Moon is near apogee. Lunar Eclipse – Moon moves into the Earth’s shadow. History of Astronomy Greeks Earth is the center of the Universe (Geocentric Model). Parallax – Point of view changes how you see things (Stellar Parallax). Proves either: A) Earth is stationary - OR - B) Stars are VERY far away. Circular Orbits Direct Motion – W -> E Motion Retrograde Motion – Backwards (E -> W) Motion Ptolemy – Came up with Epicycle model. 1500’s Nicolas Copernicus Heliocentric Model (Sun Centered) – Earth orbits the Sun with other planets. Planetary Configurations Inferior Planets –Lie between the Sun and Earth. Superior Planets – Lie beyond the Earth’s Orbit. 9/16/08 Planetary Configurations Superior Planets Tycho Brahe 1572 – Supernova 1563 – Jupiter/Saturn come close Accurate observations of planetary positions Johannes Kepler Eliptical Orbits Kepler’s Laws of Planetary Motion Law 1: Laws of Ellipses – Planets move in elliptical orbits around sun with the sun at one focus. Law 2: Law of Equal Areas – A line joining the planet and the sun sweeps out equal areas in equal amounts of time. Planets move faster when when near Perhelion then when near Aphelion. Law 3: Harmonic Law – The cube of a planet’s semimajor axis (a) is related to the square of its orbital period (p). P2=Ka3 P in earth years, a in Au then K=1. Mars: Orbital Period = 2 yrs = 4 = a = 3√4 = 1.51 9/18/08 Galileo Galilei 1609 1. Moon is not smooth 2. Sun has spots 3. Milky Way – stars 4. Venus goes through phases 5. Saturn has bulges (turns out to be rings) 6. Jupiter has moons Book: Dialogue on the two great world systems. 3 men arguing: Geocentric Model (Simplicio), Heliocentric Model, Undecided. Isaac Newton Laws of Motion: 1. Inertial Law – A body at rest or one in motion at constant speed with remain in that state unless acted on by a outside force. 2. Force Law – The force is equal to the mass of the object times its acceleration (F=ma). 3. Reaction Law – For every act there is a equal and opposite reaction. Law of Gravitation The attractive force between two objects is proportional to the product of their masses and inversely proportional to the square of the distance between them. G = Universal Gravitational Constant Centripetal Velocity √ Escape Velocity – How fast you have to move to escape a gravitational field. √ Light Electromagnetic Radiation Wave Length Nanometer – 10-9 m Frequency – Number of crests per unit of time Hertz (Hz) = Number/Sec λf = Velocity of wave = Speed of Light (in a vacuum 3 x 105 km/s) Wave-Particle Duality Particle = Energy Packet = Photon E = Constant/λ Telescope Reflection Oi = Angle of Incidence Or = Angle of Reflection Oi = Or Refraction (Bend Light) Oi = Angle of Incidence Ot = Angle of Transmission Oi ≠Ot V1 = SOL in Air V2 = SOL in Glass V1 > V2 Ot < Oi 9/23/08 Convex Lens Refracting Telescopes – Glass Reflecting Telescopes – Mirrors Newtonian Focus Cassegrain Focus Prime Focus Spherical Aberration Spherical Mirror -> Parabolic Mirror Functions of a Telescope: 1. Gather Light Proportional to Diameter2 10m KECK 5m Palomar 2. Resolution Proportional to Diameter 3. Magnification Radiation Thermal Radiation Fahrenheit (°F) Celcius (°C) 0°C – Water Freezes 100°C – Water Boils (at sealevel) Kelvin (°K) 0°K = Absolute Zero K = °C + 273 Blackbodies – Perfect emitter of radiation Wein’s Law Stefan-Boltzmann Law Spectroscopy Rainbow = Spectrum Violet – Blue – Green – Yellow – Orange – Red 400nm 550nm 700nm Types of Spectra Continuous Spectrum (All colors) Emission Spectrum (Black except for colored lines) Absorption Spectrum (Colored except for black lines) Kirchhoff’s Laws of Spectroscopy 1. Hot opaque gas liquid, or solid gives a continuous spectrum. 2. Hot rarefied (transparent) gas gives a emission spectrum. 3. Light from hot opaque source through hotter rarefied gas gives a absorption spectrum. 9/30/08 Creates Absorption Lines – Absorption of photons by electrons Creates Emission Spectrum – Emission of photons by electrons Doppler Effect Moving toward you – Shorter wavelength Moving away from you – Longer wavelength Solar System Planets Orbits the Sun Gravity pulled it into a spherical shape Cleared its neighborhood of debris 8 Planets – Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune Dwarf Planets Orbits Sun Spherical Has not cleared its neighborhood of debris 5 Planets – Pluto, Eris, Ceres, Makemake, Hauma Terrestrial Planets Jovian (Giant) Planets Planets Mercury, Venus, Earth, Mars Jupiter, Saturn, Uranus, Neptune Size Small (< 12,800 km) Large (> 49,000 km) Mass Low Large Density High -> Rocky Low -> Gases Rotation Slow Fast Distance Close (< 1.5 AU) Far (> 5 AU) Moons Few Many Rings No Yes 10/2/08 Formation of the Solar System Solar Nebula Model – Clouds of gas and dust ~4.5 billion years ago Accretation – Small objects stick together to form larger ones Protoplanets -> Planetismals -> Planets Angular Momentum – Spin motion Lost Angular Momentum 1. Interaction with early magnetic field 2. Loss of mass from system from early solar wind Extrasolar Planets – Planets around other stars. Over 200 known using Doppler Shift. Earth 3 Density – 5500 kg/m 3 Surface Density (rocks on surface) – 2000-4000 kg/m Albedo – Percent of reflected sunlight - About 37% Atmosphere Composition 78% Nitrogen (N2) 21% Oxygen (O2) Primary Atmosphere Hydrogen/Helium Escaped to space Secondary Atmosphere Volcanic Activity – Volcanism Carbon Dioxide (CO2) Water (H2O) Ammonia (NH3) Third (Tertiary) Atmosphere N2O2 Earth’s Surface (Crust) Formed 4.5 billion years ago. Oldest crust ~3.9 billion years ago Continents – 3.5 billion years old Ocean floor – 200 million years old 10/7/08 Plate Tectonics 3 Types of plate boundaries Divergent Boundary – Plates move apart o Earthquakes o Quiet Volcanism Convergent Boundary – Plates move together o Subduction – one place moves under another .
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