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Astronomy Section 6

by: Morgan Oestmann

Astronomy Section 6 ASTRO103

Morgan Oestmann

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About this Document

Segment 6
Introductory Astronomy
Michael Sibbernsen
75 ?




Popular in Introductory Astronomy

Popular in Astronomy

This 40 page Bundle was uploaded by Morgan Oestmann on Wednesday May 4, 2016. The Bundle belongs to ASTRO103 at University of Nebraska Lincoln taught by Michael Sibbernsen in Spring 2016. Since its upload, it has received 15 views. For similar materials see Introductory Astronomy in Astronomy at University of Nebraska Lincoln.


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Date Created: 05/04/16
Survey of the Solar System Summary  Common Planetary Features o What is a “planet”?  Masses, Diameters, Densities  Debris o Kuiper Belt Oort Cloud  Solar System Cosmogony o Basic Steps Condensation Our Solar System is disk-shaped and all planets have a common direction revolution An observer-looking west just after sunset can easily observer the disk- shaped nature of the solar system through the position of the planets What is a Planet?  A Celestial body that is orbit around the sun  Has enough mass/self-gravity to make itself into a round or mostly round shape  Has “cleared the neighborhood” around its orbit And the other stuff?  Dwarf Planet o Meets requirements of planet except it hasn’t cleared its neighborhood o Include Pluto and Ceres  Small Solar System Body o All other stuff that isn’t a moon Most planets in our solar system have a common direction of rotation Orbits of the planets are very close to being circular and there are two scales in our Solar System Graph of Planetary Masses Graph of Planetary Diameters Graph of Planetary Densities Graph of Planetary Rotation Periods Debris in the Solar System  Moons  Rings  Asteroids and Meteorites  Kuiper Belt Objects  Comets  Oort Cloud Radioactive Dating Solar System Cosmogony  Our Solar system formed from a gravitationally collapsing ball of gas and dust whose composition is reflected in the outer layers of the sun today  Step 2: Collapse to a Disk Observed and Uncompressed Densities Condensation Sequence  Step 3: Condensation and Accretion Two Accretion Theories  Homogeneous and Heterogeneous Accretion o We need to explain the fact that all terrestrial planets have differentiated—the high density material has sunk to the core  Step 4: Collision and Clearing The early solar system was a very violent place and a record of this is preserved on many solar system bodies Clearing of the Solar Nebula  Radiation Pressure  Solar Wind  Gravitational Slingshot  “Sweeping” of planets through their orbits Extra-Solar Planets Direct Imaging-Can we simply look and see planets around other stars —NO!! Stellar Glare IRAS  Infrared Astronomical Satellite took this image of the southern hemisphere star Beta Pictoris in 1982 Protoplanetary Disks Indirect Detection  We detect planets from “indirect evidence”—from the effects that they have on their parent star Astrometric Method  Star normally drifts in straight line in the sky  Unseen planetary companion causes it to ‘wobble’  Wobble is due to stellar reflex motion  Astrometry is art of measuring very accurate positions Planets around Pulsars Radial Velocity Techniques Doppler Wobble Tutorial 51 Pegasi Radial Velocity Curve Upsilon and Radial Velocity Curve Direct Imaging Photometric Detection  HD 209458 o Planet has two-thirds the mass of Jupiter but a 60% large radius\ Kepler uses the Transit Method  Small Effect o Terrestrial planet passing in front of a star only decreases its brightness by 1 part in 10,000  Rare Effect o Transit odds are slim—system must be aligned along our line of sight o Transits only last 2-16 hours  Verifiable Effect o All transits caused by the same planet will result in the same loss the light o Will occur every orbital period of the planet Comparative Planetology (Earth and Moon) Summary  Comparative Planetology o Earth vs Moon  Seismology o Earth’s Interiior o Magnetic Field o Plate Tectonics  Atmosphereic Retention  Meteorite Impacts  Moon o Large Impact Hypothesis Four Stages of Planetary Development  Differentiation  Cratering  Flooding  Slow Surface Evolution Seismology Earth’s Interior  Solid Core o Pressure so high metal can’t remain liquid  Liquid Core o Molten Iron and Nickel o Largely responsible for earth’s magnetic field  Mantle o Dense rock and metal in a plastic state  Crust o Outer 5 to 35 km o Floats on the mantle Convection  Magnetic Fields  Heat is transported through the liquid outer liquid core by convection. This motion of the liquid iron-nickel alloy is responsible for the Earth’s magnetic field and the process is called the Dynamo Effect. Fault Lines and Earthquakes The Earth’s Atmosphere  The Earth’s P=primeval atmosphere consisted of Hydrogen, Helium, Methane, and Ammonia. Heating from radioactive decays produced a secondary atmosphere of large amounts of carbon dioxide, nitrogen, and water vapor Retention of an Atmosphere  Escape Velocity—speed with which a particle must be travelling to escape the gravity of a planet  Velocity of a Gas—Distribution of velocities is bell shaped around an average value of:  Simulations show that to retain a gas for long periods the escape velocity should be six times the average velocity of the gas What happened to the Earth’s Primeval Atmosphere?  Hydrogen and Helium escaped into space  Ammonia, Methane, and water vapor were broken up by ultraviolet radiation  As the Earth cooled, the oceans grew through rainfall. The oceans absorbed the carbon dioxide and incorporated it into rocks.  Leaving Nitrogen! The oxygen of today’s atmosphere was produced by plants much later The Moon  The moon is only one quarter the size of the Earth o Thus it cooled very rapidly and is probably solid all of the way through o The world is a dead world—there is no atmosphere for wind erosion and no water Craters can “break” the crust Crater Features: Raised Central peaks and terraced walls Moon’s History Large Impact Hypothesis  Moon’s composition similar to earth except: o Very little iron and nickel o Very little “volatile” material  Large impact may have o Peeled off a great deal of the mantle leaving the iron-nickel core o Violence causes the volatile materials to escape Terrestrial Planets Summary  Mercury o Resonance  Venus o Runaway Greenhouse Effect  Mars o BIG features o Rovers o Atmosphere and Water Mercury Resonance  PRotation9 days  PRevolution days  A 2:3 resonance—revolves twice for every three times it rotates. This is due to the ling history of gravitational interactions with the sun  This slow rotation leads to a tremendous temperature differential between the side facing the sun (700 K) and the dark side (100 K) Mercury photographed by a ground-based telescope Mercury photographed by the Mariner 10 Spacecraft in the 1070s Mercury and the Moon compared  Mercury resembles Earth’s moon o Airless, waterless, dead world o Cratered, but less than the moon o With fewer maria, no evidence of rilles  Rilles- Rivers of lava Scarps—Huge cliffs Venus  Picture in the UV  Dense atmosphere  Highly reflective= bright planet Atmosphere of Venus—Dense Carbon Dioxide Venera 13 Photograph of Venus True Color Picture of Venus Mars Observing Mars  Why was 2003 a good year to observe Mars? o Mars was near opposition!  Planets have elliptical orbits  Eccentricity o E Earth 0.017 o E Mars 0.093 Big Volcanoes and Olympus Mons Mars Exploration Rovers 360 View from Spirit A Thin Atmosphere and Dust Devils  95% Carbon dioxide  <1% the density of earth’s atmosphere Martian Moons


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