Exam 2 Study Guide
Exam 2 Study Guide AY 101
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This 5 page Study Guide was uploaded by Alyssa Hendrixson on Friday February 20, 2015. The Study Guide belongs to AY 101 at University of Alabama - Tuscaloosa taught by Dean Martin Townsley in Winter2015. Since its upload, it has received 149 views. For similar materials see Introduction to Astronomy in Physics 2 at University of Alabama - Tuscaloosa.
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Date Created: 02/20/15
HY 102 Exam 2 Study Guide Planets around other Stars Nearly all of the planets spin in a similar direction to their orbit the exceptions being Venus and Uranus The inner 4 planets in our solar system are small and rocky and the outer planets are gas and ice giants Asteroids are made of rock and metal while cometary bodies contain a lot of hydrogen ice compounds in addition to rock and metal The sun spins the same direction as the planets orbit because that was the dominant direction of spin of the material out of which all of the Sun and planets were formed Planetary composition is largely determined by the local temperature of the protoplanetary disk This temperature controls what can condense in that region of the disk and form planets there Asteroids are made of rock and metal while cometary bodies contain a lot of hydrogen ice compounds in addition to rock and metal There are three major methods of finding planets Direct imaging which has only found a few planets directly images the planet and star The transit method is used to observer the planet blocking a small amount of the star39s light when it passes in front of the star The Doppler shift method measures the shift in wavelength of the star39s light as it moves in response to the gravity of the planets around it Graphs of spectra indicate the relative intensity of light of various wavelengths Spectra with an intensity increasing to shorter wavelengths is quotbluequot Spectra with intensity increasing as wavelength increases is quotredquot Spectra in which intensity does not change much with waving is quotwhitequot These correspond to how we visually perceive these types spectra with these corresponding shapes in optical wavelengths Light with a higher relative intensity at shorter wavelengths will have a higher average energy per photon This is true regardless of quotbrightnessquot which is instead related to the total number of photons per unit time Absorption lines are wavelengths at which the power in the spectrum is small compared to the power other wavelengths They appear as sharp dips in a plot of power vs wavelength An absorptionline spectrum is formed when light from a source with a continuous spectrum such as a thermal radiation source passes through a cool lowdensity gas Light is absorbed by the atoms in the gas only at specific wavelengths creating dark quotabsorption lines39 in an otherwise smooth spectrum There are three major types of spectra A continuous spectrum emitted by a hot solid contains light of all wavelengths An emission line spectrum emitted by a hot lowdensity gas contains light mostly at just a few specific wavelength An absorption line spectrum generally created by passing a continuous spectrum HY 102 Exam 2 Study Guide through a lowdensity cloud of gas or emitted by a star contains light at most wavelengths but a few specific wavelengths have much weaker intensity Greenhouse Effect If an object is moving toward the observer spectral lines appear to the observer to be shifted to shorter wavelengths blue shifted If it is moving away from the observer spectral lines appear shifted to longer wavelengths red shifted The amount of Doppler shift observed from a star with a planet around it also depends on how the orbit is oriented If we observe the orbit from directly above the orbital plane there is no Doppler shift Measurements of planets around other stars show that planetary systems like ours are most common around Sunlike stars with planets in nearly circular orbits and rocky planets near their star and giant planets further away However some planetary systems are quite different having giant planets near their star as close as or closer than Earth or even Mercury and sometimes in noncircular orbits When planets were first found around other stars due to the inability of Doppler shift techniques to find small planets giant planets were found with a significant number close to their star This is quite different from our own solar system in which the giant planets are distant from the Sun While the transit method can determine the physical size of a planet the Doppler shift method can determine its mass Before 2011 almost no planets with masses similar to Earth had been found around other stars This is not because they aren39t there but because the techniques available to find them measuring the velocity of the stars they orbit was not sensitive enough to find such small planets easily Rocky Planet Atmosphere and Interior The atmospheres of the rocky planets are continuously replenished by volcanic outgassing from their crust Given objects emitting light with a thermal spectrum a higher temperature object will emit radiation with a peak in intensity at a shorter wavelength A lower temperature object39s spectrum will have a peak intensity at longer wavelengths The Earth39s atmosphere absorbs strongly at wavelengths including ultraviolet and infrared but is mostly transparent to visible light Most of the energy in the Sun39s light 90 is in the visible and infrared wavelength ranges Also most of the ultraviolet light from the sun is absorbed by the atmosphere As a result any changes in the amount of ultraviolet light emitted by the Sun would have relatively little effect on the energy received at the surface of the Earth HY 102 Exam 2 Study Guide 0 Due to its temperature the Earth39s surface emits infrared light 0 While a modest amount about a quarter of the energy arriving at Earth as sunlight is absorbed by the atmosphere nearly all of the light more than three quarters that is emitted by the Earth39s surface is absorbed by the atmosphere instead of escaping to space This is because much of the energy in sunlight is in the visible wavelengths and is therefore not absorbed by the atmosphere but all of the energy emitted by the Earth39s surface is in infrared wavelengths and is therefore strongly absorbed by the atmosphere 0 Greenhouse gases in the Earth39s atmosphere cause much of the infrared light emitted thermally by the Earth39s surface to be absorbed by the atmosphere and then emitted back toward the surface of the Earth This quottrappingquot of energy at the Earth39s surface makes the surface temperature warmer than it otherwise would have been without an atmosphere An increase in a greenhouse gas such as water or carbon dioxide will increase the energy absorbed by the atmosphere and therefore increase what it radiates back down toward the Earth and thus increase the surface temperature 0 Internal heat and its movement toward the surface is the source of geological activity in rocky planets Geological activity tends to remove surface craters via lava flow volcanic activity and crustal movement 0 Small planetary bodies cool fast causing their geological activity to cease While no liquid water currently exists on Mars39 surface longlived liquid water existed on the surface in the distant past 0 The cooling of Mars39 interior caused its climate to change drastically about 3 billion years ago This was mainly due to less atmosphere as a result of both a smaller magnetic field and less outgassing from volcanic activity 0 The high carbon dioxide content of Venus39 atmosphere is in part due to the absence of liquid water Liquid water dissolves carbon dioxide from air and allows it to be incorporated into rocks 0 Among the rocky planets Earth is the only to exhibit plate tectonics Others exhibit some evidence of volcanoes craters and erosion typically by wind Nature of Matter and Age of Earth 0 The nucleus of an atom is very small compared to its overall size The size comes mostly from the region over which the electron quotcloudquot is spread The name of an element is related to the number of protons in the nucleus This is the number that increases one by one lefttoright and toptobottom on the periodic table This is also the number of electrons that an atom of this element generally has and determines the chemical properties of the element 0 The total number of protons and neutrons is indicated by saying a number after the name This indicate the isotope of a particular element The number of HY 102 Exam 2 Study Guide protons and neutrons can be inferred from its name and isotope number For example carbon14 also written 14C has 6 protons and 8 neutrons for a total of 14 protons and neutrons Argon is an example of a material that does not become part of rocks when they form because it is a nonreactive gas rather than a solid 0 The halflife of a radioactive isotope is the time it takes half of a given initial quantity of the radioactive material to change into another material by decaying A rock can be dated by comparing the amount of a radioactive isotope to the amount of its decay product in the rock The amount of the first isotope decreases over time and the amount of the product increases At the halflive there is an equal amount of radioactive and product material Gas and Giant Planets review Planetary composition is largely determined by the local temperature of the protoplanetary disk by controlling what can condense there The location in the presolar disk outside of which ices can condense is called the frost line or snow line 0 The outer planets have similar mass cores of rock metal and ice compounds but differ in that Jupiter and Saturn have much more hydrogen and helium than Uranus and Neptune Internal heat particularly its transfer to the surface drives atmospheric behavior quotweatherquot on giant planets Both Solar heat and rotation also have a role on rocky and giant planets Internal heat drives geological activity on rocky planets not weather 0 The color of an object is determined by the dominant wavelength of the light it scatters Any wavelengths that are absorbed are then absent low intensity in the resulting spectrum 0 The various bands on Jupiter are different colors because the condensed droplets forming the cloud layers visible in one region have a different material composition than another layer Not all regions have all cloud layers depending on whether the air is rising or falling in that region 0 Although Jupiter39s large moons are small enough and old enough to have cooled and become geologically dead the large moons in orbits closest to Jupiter are heated by tidal forces due to their noncircular orbits around Jupiter 0 The rings of the giant planets are made up of many icy chunks of a wide variety of sized from the size of dust up to bodies few meters across 0 The particles in the giant planet rings are continuously created by impacts on and descriptions of small moons and are destroyed by micrometeorite impacts grinding them to smaller particles Asteroids and Comets HY 102 Exam 2 Study Guide Pluto Asteroids are made of rock and metal while cometary bodies contain a lot of hydrogen ice compounds in addition to rock and metal Asteroids formed in the inner portion of the protoplanetary disk which was too hot for hydrogen ice compounds to condense inside the frost line and so have almost no icy compounds Cometary bodies formed in the outer portions of the protoplanetary disk which were cool enough for hydrogen ice compounds to condense outside the frost line and therefore have a composition rich in these ices A planet in an elliptical noncircular orbit does not move at constant speed during its orbit It moves fastest at the point in the orbit nearest the star and slowest at the point in the orbit farthest from the star This motion sweeps out equal area in equal time Comets we see today come from the Oort cloud or the Kuiper belt Comets must be near the Sun in order for the solar wind and radiation to be strong enough to strip material gas and dust from the comet This stripped material creates the comet39s tail etc As bodies planets or asteroids differentiate dense elements like metals will tend to move to their centers while less dens material like rock will tend to move toward their outsides This will not be a clean separation but just a shift in relative concentration of certain materials Since the temperature decreases with distance from the star an overall hotter protoplanetary disk causes the frost line whose temperature is always the same about 150 K to be farther away from the star for a hotter disk and closer for a cooler one Regardless of their current location bodies formed in the inner solar system are rocky while those formed in the outer solar system are icy The transNeptunian quotbeyond Neptunequot bodies orbiting farther from the sun than Neptune As a result of forming far out in the solar system they are icy Kuiper belt objects were formed near their current orbits In contrast objects in the scattered disk and Oort cloud were scattered onto their current orbits by interaction with the planets When initially discovered around 1930 Pluto39s mass was greatly overestimated due to it reflecting a large fraction of the sunlight that hits it Pluto39s mass wasn39t know until 1978 when its moon was discovered The moon39s orbital properties distance from Pluto and period allowed a measurement of Pluto39s mass
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