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Frontiers in Astronomy- Week 6

by: Kathryn Notetaker

Frontiers in Astronomy- Week 6 PHY 21430

Marketplace > Kent State University > Physics > PHY 21430 > Frontiers in Astronomy Week 6
Kathryn Notetaker
GPA 3.3

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About this Document

Week 6 notes from both lectures.
Spyridon Margetis (P)
Class Notes
EARTH, astronomy, Greenhouse effect, ozone
25 ?





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This 5 page Class Notes was uploaded by Kathryn Notetaker on Friday October 7, 2016. The Class Notes belongs to PHY 21430 at Kent State University taught by Spyridon Margetis (P) in Fall 2016. Since its upload, it has received 5 views. For similar materials see FRONTIERS IN ASTRONOMY in Physics at Kent State University.


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Date Created: 10/07/16
Frontiers in Astronomy Week 6 Earth  Overall structure  2 part core  solid inner core- 1300 km in radius  liquid outer core- 3500 km in size  Mantle- topped by a thin crust  Hydrosphere (oceans)  atmosphere  magnetosphere  Earth’s Atmosphere  made up 80% of nitrogen and 20% of oxygen  small amounts of noble gasses : carbon dioxide and vapor  starts with troposphere (contains life)  stratosphere: ozone layer  mesosphere  ionosphere  exosphere  most of the atmosphere except troposphere is at the freezing or below freezing temperatures  troposphere contains weather and all phenomenon important to life forms  Convection  hot lighter air rising resulting I circulation currents- as air gets warm near the surface tends to get lighter and therefore rise, making space for cool air to come done  depends on warming of the ground by the sun  circulating air creates winds and weather in general  Ionosphere  (ion) contains ionized atoms-electrons removed from atoms- by high energy part of solar radiation bc it is the first thing the high energy part of the solar radiation encounters  good conductor for electricity  reflects radio waves in the AM range- why we can hear AM stations well beyond the horizon  it is transparent to FM and TV- need re-transmitters  Ozone Layer  in stratosphere below the mesosphere  absorbs ultraviolet radiation  recently found that CFC’s (found in older air conditioner coolants) have been damaging the ozone layer resulting in ozone hole  a single chlorine atom can destroy about 100,00 ozone molecules  the effect is maximum during the Antarctic spring (~50%) but present everywhere  ozone layer gets thinner in every part of the world-not to such extent as Antarctica  Surface Heating  Albedo-characterizes the reflectivity of any surface  earth reflects 30-35% (has an albedo) of incoming radiation back to space  sunlight that is not reflected or absorbed by the atmosphere is absorbed by Earth’s surface, warming it  Surface re-radiates as infrared thermal radiation  atmosphere absorbs some infrared causing further heating  this is known as the greenhouse effect- initial radiation that comes and hits a surface it gets transformed into infrared radiation that gets trapped in some place  same phenomenon happens in greenhouses- as the radiation passes through the plastic, gets transformed into infrared radiation heats up and makes plants grow  Greenhouse Effect and Global Warming  one result of modern society has been to increase CO2 levels in the atmosphere  a corresponding increase in global average temperature has been seen as well- called the hockey stick effect from its shape  unknown how much the temperature will continue to increase  depends on us  Possible consequences of global warming  rise in sea level (melting of glaciers/polar ice caps)  more severe weather extremes (heat waves or storms)  Crop failures ( as climate zone change)  expansion of deserts  spread of tropical diseases away from tropics  Why is the Sky Blue?  scattering of light by air, depends on wavelength of light  wavelength of blue light is closer to the size of air molecules so it is scattered most strongly  as white light comes from the sun, the blue part of the spectrum is scattered in the atmosphere which gives it the color  this phenomenon comes when the sunlight is at is strongest (noon)  Why is the evening sky red?  when the sun is close to the horizon, light has to travel much more atmosphere than when the sun is up, so the light is scattered most  as the sun sets light has to come to the lower part of the atmosphere, which contains dust  the more dust, the more scattering of light happens  The length of the atmosphere + that part of the atmosphere contains dust (scatters more light)= giving a red glow in the sky  History of Earth’s atmosphere  primary atmosphere was mostly containing hydrogen, helium, methane, ammonia and vapor slowly escaped earth’s gravity over a period of half a billion years  secondary atmosphere was formed from volcanic activity mostly nitrogen  life appeared in the oceans, creating atmospheric oxygen and ozone  ozone protected surface from UV so life could spread to land producing oxygen  Earth’s interior  much harder to probe than atmosphere, use seismic waves (earthquake) to probe it  Seismic waves:  Earthquakes produce both pressure and shear waves Pressure waves: longitudinal and can travel through both liquids and solids Shear waves: transverse and will not travel through liquid, liquid does not resist shear forces  wave speed depends on the density of the material  we can use pattern of reflections during earthquakes to deduce the interior structure of earth  many earthquakes happen= a vast amount of data about the interior  patterns will depend on nature and size of different parts  our knowledge is based on such indirect observations and modeling  Current accepted model mantle is much less dense than core mantle is rocky core is metallic- iron and nickel outer core is liquid inner core is solid due to pressure inner core has same temperature as sun’s surface hypothesis verified by volcanic lava which comes from mantle, allows analysis of composition  History  earth was probably molten when formed and re-melted due to bombardment by space debris  heavier materials sank to center, this gravitational energy produced extra heat  radioactivity provides a continuing source of heat  Radioactive dating  technique used to find out how old a specimen is  number of protons in a n atom’s nucleus determine which element it is  different isotopes of the same element have the same number of protons but different numbers of neutrons  many of these isotopes are unstable and undergo radioactive decay  characterized by a half-life (time it takes for half the atoms decay  picture  at 0, the whole sample is present  at half time only 50% of sample will survive  as time goes on less and less of material is present  half lives  measured laboratory for almost all known isotopes  we can use them for determining the age of samples by looking at isotope ratios  most useful isotope for dating rock samples is uranium 238 which has a half-life of 4.5 billion years, comparable to the age of the earth  the dating process involves measuring the ratio between parent nucleus and the daughter nucleus (lead 206)  ex. the uranium contains 50% of lead 206, then we know that about a half- life (4.5 billion years) have passed  the most ancient rocks on earth dated at ~4 billion years  Surface Activity  earthquake and volcanic activity on earth’s surface is not random, outlines certain region of earth’s crust (tectonic plates)  some plates collide (urasion plate and pacific plate) and some move away from each other (African and north/south American plates)  continental drift- the fact that earth’s surface is covered with crustal plates which can move independently  at plate boundaries, earthquakes and volcanoes occur  plates (slabs of earth’s surface) may contain continents (land)  Nazca plate west of Chile  plates move a few centimeters a year  What drives plate motion?  driven by convection (analogous to atmospheric one but much slower)  happens because something very hot (interior of earth) and something cooler(atmosphere of air)  as plates collide one can slide below the other or raise the other one  subduction zone- one plate slides below another, volcanic activity likely to happen  high mountains result from a plate colliding that raises it  Himalayan  Faults  plates slides along each other, earthquakes occur  pacific and north American plates rub each other creating the San Andreas fault  Rifts-plates moving away from each other  African plate moving away from American plate creating a rift in the middle  Pangaea  the continents merged into one, if we follow the continental drift backwards  Earth’s magnetosphere  weak magnetic field  created by the moving molten interior of earth (dynamo theory)  oriented close to the earth’s rotational axis  the north magnetic pole is CLOSE to earth’s north pole  same with south pole  crust created at rift zones preserves the magnetic field present at the time it solidified  can tell that field reversals occur about every 500,000 years north pole becomes south magnetic pole we have signs that we are entering an era of field reversal  magnetosphere- the region around earth where the charged particles coming from the solar wind are trapped (magnetic bottle effect)  relative size to earth  these charged particles are trapped in areas called the van Allen belts  near the poles, the van Allen belts intersect atmosphere  charged particles can hit and excite air atoms, as they excite they emit light of different color (Aurora)  Aurora Borealis  The tides  due to the gravitational force on earth from the moon  force on the near side of earth is greater than force in the far side  water can flow freely in response  from geometry and length of day we can find that going from high to low tide takes about 6 hours  the sun has a less effect, because it is farther away  when the sun-moon are aligned with earth (full or new moon) tides are stronger (spring tides)  when normal (first/third quarter) weaker tides (neap tides)  Interesting detail  tides tend to exert a drag force on earth, slowing its rotation  gradually makes the earth day longer and longer  this will continue until the earth rotates synchronously with the moon, the same side of the earth always points towards the moon  at that point, the earth day is going to be about 47 times of the current earth day  Summary  Earth’s structure from inside out: core, mantle, crust, hydrosphere, atmosphere, magnetosphere  atmosphere is mostly nitrogen and oxygen; thins rapidly with increasing altitude  greenhouse effect keeps earth warmer than it would otherwise be  study interior by studying seismic waves  crust is made of plates that move independently  movement at plate boundaries can cause earthquakes, volcanic activity, mountain ranges and rifts  new crust formed at rifts shows evidence of magnetic field reversals  earth’s magnetic field traps charged particles from solar wind  tides are caused by gravitational effects of moon and sun


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