AST 301Introduction to AstronomyJohn LacyRLM [email protected] LiRLM [email protected] JeonRLM [email protected] site: www.as.utexas.eduGo to Department of Astronomy courses,AST 301 (Lacy), course websiteRearranged schedule for next few weeksThis week: Introduction to planets and a bit of geologyNext week: Planet formation and a bit on small bodiesThird week: Atmospheres9/27 Ch 710/4 Ch 8 (Prof. Dinerstein)10/11 Ch 1010/18 Ch 13 (back on schedule)Topics for this weekDescribe and compare briefly the compositions and orbits ofthe terrestrial planets, Jovian planets, asteroids, andcomets.What is inside of the terrestrial planets?What determines the appearances of the surfaces of theterrestrial planets?How do we determine the age of the planets?Photon energiesWhen an atom emits a photon, the atom loses the amountof energy the photon carries off.Since atoms can only have certain energies, they can onlyemit photons of certain energies.The photon energy must equal the different between twoallowed amounts of atom energy.hf = photon energy = change in atom energy = differencebetween two allowed amounts of atom energyDoppler shiftIf an object emitting light (or sound) waves is movingrelative to an observer, the observed wavelength isdifferent from that emitted.If the emitter moves toward the observer (or the observermoves toward the emitter) the observed wavelength isshorter than the emitted wavelength.If the emitter moves away from the observer, the observedwavelength is longer than the emitted wavelength.If the motion is small compared to the speed of the wave(the speed of light for light waves) the formula for theshift in wavelength is:(λobserved-λemitted) / λemitted = v / cQuizThe Earth orbits around the Sun with a speed of 30 km/s.The speed of light is 300,000 km/s.I observe infrared radiation from sulfur atoms which isemitted at a wavelength of 10 µm.What is the difference between the emitted wavelength andthe wavelength I observe from the moving Earth?A. .001 µmB. .030 µmC. 30 µmD. 100,000 µmTerrestrial PlanetsThe inner four planetsSizes similar to the Earth’sInteriors made of metals and rocksVery thin atmospheres (compared to the diameters of theplanets)Earth also has oceans (and Mars may once have). Thesealso make up a small fraction of the volume.Jovian planetsThe next four planetsDiameters about 10 times the terrestrial planets’Interiors made of ices and gasses (probably with smallrocky cores)Jupiter and Saturn are mostly gas.Uranus and Neptune are mostly (partially melted) ices.“Flying” over VenusThe video was made from radar data from Venera andMagellan orbiters.Brightnesses correspond to radar reflectivities (generallyroughnesses).The vertical scale is exaggerated by a factor of 10.Most of the features are volcanic: domes, lava flows, andcalderas.Others are impact craters.Without liquid water, there is less erosion on Venus, socraters are more common and prominent than on Earth.Mars movieThe data are from the Viking orbiters.Vertical scale is exaggerated by a factor of 5.The “flight” goes over Valles Marineris, the Tharsisvolcanoes, and Olympus Mons.Valles Marineris may have been cut by water, and is 1800miles long.Olympus Mons is 15 miles (75,000 ft) high and as wide
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