Astronomy - Earth and its Moon - Quick Guides

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Study GuideAstronomy–Earth and its Moon1. Earth's AtmosphereEarth is surrounded by a thick blanket of gases called theatmosphere.This atmosphere protects life and controls weather and temperature.Scientists divide the atmosphere intofour main layers, based on how temperature changes withheight.1.1The Troposphere (Lowest Layer)Thetroposphereis the lowest layer of the atmosphere and is closest to Earth’s surface.This is the layerwhere we live and where weather occurs.•Air in this layer is constantly moving due toconvection currents•This movement causesclouds, rain, winds, and storms•Air density decreases quickly as height increases•The main source of heat isconductive heating from the ground•Heat is lost throughradiation and mixing of airBecause of these processes,temperature decreases rapidly as altitude increasesin thetroposphere.1.2The StratosphereAbove the troposphere lies thestratosphere.•This layer containsstrong horizontal winds, known as thejet stream•These winds influence weather patterns at Earth’s surface•Ozone gasin this layer absorbs harmfulultraviolet (UV) radiationfrom the SunAs a result, the stratosphere plays a major role inprotecting life on Earth.

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Study Guide1.3The MesosphereAbove the stratosphere is themesosphere.•Oxygen and ozone absorbsolar ultraviolet radiation•Energy is lost throughradiation and air mixing•At the base of the mesosphere, around50 km above Earth, temperature reaches alocalmaximumThis balance between energy gain and loss defines the mesosphere.1.4The Thermosphere and IonosphereThethermospherelies above the mesosphere.•Very short-wavelength solar radiation is absorbed here•There are very few air particles, so absorbed energy leads tovery high temperaturesThelowest part of the thermosphere(from about80 km to 400 km) is called theionosphere.•Gases are ionized by solar radiation•This layerreflects radio waves, helping long-distance communication•Meteors burn upin this regionFar above this, theexosphereslowly fades into outer space.

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Study Guide1.5The Coriolis Effect and Global WeatherEarth rotates on its axis, and this rotation affects air movement.•All points on Earth rotate once every 24 hours•Theequator travels fasterthan the poles•Air moving north or south keeps its original eastward speedThis causes theCoriolis Effect, which makes air appear to curve:•In theNorthern Hemisphere, air moving toward low pressure rotatescounterclockwise•In theSouthern Hemisphere, it rotatesclockwise•Air moving away from high pressure rotatesclockwise in the Northern HemisphereThis effect plays a major role inwinds, storms, and hurricanes.1.6Importance of the AtmosphereThe atmosphere is essential for life because it:•Reduces extreme temperature changes across the planet•Protects Earth from harmfulultraviolet radiation•Supplies essential gases likeoxygen and carbon dioxide•Helps maintain a stable climate1.7The MagnetosphereThemagnetosphereis the region of space around Earth controlled by Earth’smagnetic field.•It protects Earth from harmful charged particles from the Sun•Inside it are two doughnut-shaped regions called theVan Allen belts•These belts trap charged particles from thesolar windSome of these particles travel along magnetic field lines and enter the atmosphere near the poles,creating theaurora(Northern and Southern Lights).The solar wind stretches the magnetosphere into along tail opposite the Sun.

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Study GuideOther planets with magnetic fields also have magnetospheres.1.8The Greenhouse EffectEarth is warmer than expected because its atmospheretraps some heat.•Sunlight heats Earth’s surface•The surface gives off heat asthermal radiation•Some of this heat isabsorbed and re-emitted by atmospheric gasesThis process is called thegreenhouse effect.Gases that contribute to this effect include:•Carbon dioxide (CO₂)•Water vapor (H₂O)•Methane (CH₄)•Chlorofluorocarbons (CFCs or freons)Because of the greenhouse effect, Earth’s average temperature is about300 K (80°F)instead of250K.Venus shows an extreme example of this effect due to itsvery dense CO₂atmosphere.

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Study GuideSummary•The atmosphere hasfour main layers•Weather happens in thetroposphere•UV protection comes from thestratosphere•Meteors burn in thethermosphere•Themagnetosphereshields Earth from solar wind•Thegreenhouse effectkeeps Earth warm enough for life2. Earth's Chemical ComposiƟon2.1What Is Earth Made Of?Earth is made up of different materials, both in itsatmosphereandinside the planet itself.Scientists study these materials to understand how Earth formed and how it works today.2.2ComposiƟon of Earth’s AtmosphereThe atmosphere is the layer of gases surrounding Earth. Its composition is fairly stable and includes:•78% nitrogen (N₂)•21% oxygen (O₂)

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Study Guide•1% argon (Ar)In addition to these main gases, there arevery small (trace) amountsof:•Carbon dioxide•Water vapor•Other gasesEven though these gases are present in small amounts, they play an important role in weather,climate, and life on Earth.2.3Chemical ComposiƟon of Earth’s Surface RocksWhen scientists directly analyzerocks found on Earth’s surface, they discover that they are mainlymade of the following elements, listed from most to least abundant:1.Oxygen2.Silicon3.Aluminum4.IronThese surface rocks have anaverage density of about 2.7 g/cm³, meaning they are relatively lightcompared to Earth as a whole.2.4Earth’s Density: A Big ClueAlthough surface rocks are not very dense, theaverage density of the entire Earth is muchhigher—about 5.5 g/cm³. This difference leads to two very important conclusions.2.5What Does This Tell Us About Earth’s Interior?The Inside of Earth Is Much DenserThe high overall density means Earth’s interior must containmuch heavier materialsthan thosefound at the surface.•The pressure from overlying rocks does compress materials inside Earth.•However, compression alone isnot enoughto explain the high density.•This means Earth’s interior must containnaturally dense elements, especiallyiron andnickel, which are also common in the universe.

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Study Guide2.6Earth Was Once Very Hot and MoltenThe clear separation between:•lighter materials on the outside, and•heavier materials in the centersuggests that early in Earth’s history, the planet waspartially or fully molten.When Earth was hot and molten:•Heavy elements like iron and nickelsank toward the center.•Lighter materialsrose toward the surface.This process is calledchemical differentiation, and it explains why Earth has layered internalstructures today.Key TakeawayEarth’s chemical composition—both at the surface and deep inside—gives us strong evidence thatthe planet:•Has adense, metal-rich interior, and•Went through ahot, molten phase early in its historyThese insights help scientists understand not just Earth, but how other planets may have formed aswell.3. Interior Structure: Core, Mantle, Crust3.1How Do We Study Earth’s Interior?We cannot directly see or drill deep into the Earth. Instead, scientists studyearthquake wavestolearn about what lies inside our planet.When an earthquake occurs near the Earth’s surface, it sends out two main types of waves:•Pressure (P) waves, which move back and forth•Transverse (S) waves, which move side to side

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Study GuideAs these waves travel through the Earth, their paths bend due torefraction, because different layershave different densities and properties. By carefully measuring thearrival times of these wavesatseismographic stations around the world, scientists can determine thedensity, temperature, andpressureinside the Earth.3.2Main Layers of the EarthEarth has three major internal layers:1.Crust2.Mantle3.CoreEach layer has unique physical and chemical properties.3.3The CrustThecrustis the thin outermost layer of the Earth. It includes:•Continents•Ocean floorsEven at its thickest, the crust is only about30 kilometers deep, which is very thin compared toEarth’s total size.3.4The MantleBeneath the crust lies themantle, which is much thicker and denser.•Theuppermost mantlebehaves like a solid and, together with the crust, forms thelithosphere, which is about80 kilometers thick.•Below this lies theasthenosphere, where mantle rocks areplastic or malleable.•This means the material canslowly flow under pressure, even though it remains solid.

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