Astronomy 311: Revision• Gravity– Newton’s law of gravity:F =GM1M2R2,where G is the gravitational constant.– A more accurate treament is the theory of general relativity whichtalks about gravity being due to the curvature of spacetime.– An observational test is observation of the precession of the perihelionof Mercury.– Newton’s law of gravity leads to Kepler’s laws of motion. Kepler’sthird law states thatP2=4π2a3G(M + m).If M is much bigger than m then in appropriate units P2= a3.– An N body calculation is a way of calculating the dynamics of theSolar System.– What are Lagrange points.– Orbital resonances, Kirkwood gaps, Dynamics of ring systems, shep-herd moons, gap moons. Synchronous rotation. Planetary migration.– Milankovitch cycles: eccentricity, obliquity and precession.– perihelion, aphelion, eccentricity.∗ Terrestrial Planets· Core mantle, crust structure of terrestial planets.· Lithosphere.· Differentiation.· Geological activity - how interiors get hot, accretion, heat fromdifferentiation and radioactive decay.· Interior co oling: conduction, convection and radiation - whichis the most impo r t ant in the Earth’s interior?· Mantlel convection cells.· Role of planetary size in cooling: surface area of a sphere 4πr2,volume o f a sphere43πr3.· Requirements for a planetary magnetic field - which planetshave reasonable magnetic fields and why?1· Why do terrestrial planets have different geological histories?Size, distance from Sun and r otation.· four types of processes that shape planetary surfaces: crater-ing, volcanism, tectonics and erosion.· Outgassing by volcanos.· Terrestrial planet magnetic fields.∗ Terrestrial Planet Atmospheres· Whats an atmosphere?· Which of the terrestrial planets have atmospheres?· Atmospheric pressure, ideal ga s lawPρ= RT . Generally con-tracting/expanding gases heat up/cool down.· How can atmospheres affect planets?· Greenhouse effect - name some greenhouse gases.· Planetary temperatures are affected by planet’s distance fromthe Sun and the planet’s overall reflectivity.· NoteT = 280 ×4s1 − refd2K,where ref is the reflectivity or albedo and d is the distance ofthe planet from the Sun. This is a slight modification of theStefan-Bolztmann law: L = 4πσR2T4.· This entails the inverse square law, surface area of a sphere,concept of reflection and absorption of radiation and the blackbody spectrum.· Variation of atmospheric properties with latitude: troposphere,stratosphere, thermosphere and exosphere.· What types of radiation can pass through these atmosphericlayers.· Xrays, UV, Visible and IR.· Ionization, dissociation transmission and absorption.· Reflectivity and Absorption· Scattering of light by the atsmphere: why is the sky blue, whyare sunsets red.· Heating of the troposphere by IR light from the ground af-ter visible light heats up the ground. Temperature inversionfurther up. Temperature structure of the atmosphere, convec-tion.· Earth is unique in having a stratosphere. Ozone - lack ofconvection.2· Whats the ionosphere?· X rays and the upper atmosphere.· Temperature profile of the atmosphere.· Comparative structure of terrestrial planet atmospheres.· Circulation cells in the Earth’s atmosphere with and withoutthe effect of the Coriolis f orce.· The coriolis force - what it is and how does it affecct thecirculation cells in the Earth’s atmosphere.· Water cycle on the Earth, CO2cycle.· Factors affecting long term climate change: solar brightening,axis tilt, reflectivity and greenhouse gases.· Volcanic outgassing as the primary souce of terrestrial planetatmospheres.· Thermal escape, Vesc=q2kT/mH>· Thin atmosphere of the moon and mercury - why?· History of Martian atmosphere - change in magnetic field?How could this have affected its atmosphere.· Solar wind, magnetosphere etc.· Strong greenhouse effect on Venus.· Earth’s pleasant atmosphere, the CO2cycle.· Seasons on Earth, further out, ellipticity also affects severityof seasons eg. Mars’ elliptical orbit.∗ Jovian Planet Systems· Rotation and shape.· Dependence of radius on mass for a jovian planet - self com-pression.· Composition - frost line.· Basic structure: rocky core, metallic H, liquid H, gaseous H,cloud tops.· Comparative structure of Jovian planets.· Internal heat sources - helium rain.· Atmospheric structure on Jupiter: water, ammonium hydro-sulfide and ammonia clouds. Their respective colors and why.· Temperature structure.· Comparative jovian planet atmospheres.· Magnetospheres on jovian planets - bow shock, mag netopause- relation of magnetic NS axis to rotation axis.· Jovian satellites, ring systems.3· Sun, structure (core, radiative zone, tachocline, convectivezone, chro mosphere, corona, fusion, approxiamete age andlifetime. Magnetic field, differential rotation, sunspots, solarcycle.· Hydrostatic equilibrium, solar thermostat.· Helioseismology: n, l, m. ”p” and ”g” modes. Dep endence onsound speedqP/ρ. Tachocline.· Solar dynamo: motor and generator - comparison to geody-namo.· Solar wind, composition, typical speeds, interaction with otherplanetary magnetic fields. Interaction of the solar magneticfield with interstellar space. Interplanetary magnetic field.∗ Asteroids and Comets.· Meteors, meteorites.· Comets: nucleus, coma, plasma, dust tail. KBO and OOcharacteristics. Origin of KBO’s and OO’s and this relationto their current position.∗ Extra-Solar planets· Electromagnetic radiation, wavelength, speed of light, spec-trum, energy levels, continuous and discrete spectrum, spec-tral lines. Doppler shift,λobs− λrestλrest,blueshift and redshift.· Astrometry, Transits, Doppler method for detecting planets.Advantages/disadvantages of each. Evidence for planetary