Follow the Energy: Follow the Energy Lecture 7 The Sun


Slide2: ATP Every living cell uses ATP (adenosine triphosphate) to store and release energy Energy in Energy out


Slide3: How does life extract the energy? Photosynthesis CO2 + H2O + h (Energy) → CH2O + O2 In reality: 6CO2 + 6H2O + h (Energy) → C6H12O6 + 6O2 Respiration CH2O + O2 → CO2 + H2O + Energy In reality: C6H12O6 + 6O2 → 6CO2 + 6H2O +Energy


Slide4: Solar Radiation: The source for 99.9% of Earth’s energy NASA/ESA SOHO


Slide5: ~4.6 billion years old G2 class star (~8% of stars are G class) based on photospheric (stellar surface) temperature >100 million stars are of the same class in our galaxy Not only supports almost all life on Earth via photosynthesis but also drives the Earth’s climate and weather The Sun


Slide6: The Sun – Basic Facts Distance from Earth 1 AU = 1.5*108 km Travel time for Light to Earth About 8 minutes Travel time for solar wind to 1 AU A few days Mean surface temperature 5800K (~11,000 oF) Temperature in the Center 1.55x107 K (~28,000,000 oF) Temperature in the Corona A few million K


Slide7: Sun seen in Xrays The Sun – Basic Facts Mass 333,000 Earth Masses 99% mass of the Solar system Diameter 103 Earth Diameters Average Density 1410 kg/m3 Composition (by mass) 74% Hydrogen, 25% Helium, 1% other elements


Slide8: Sun is in a hydrostatic balance – neither expands nor shrinks Gravitational force is balanced by the energy from thermonuclear fusion


Fusion Reactions: Fusion Reactions Chemical reactions – elements (nuclei) do not change just repartition: 6CO2 + 6H2O + h (Energy) → C6H12O6 + 6O2 Number of carbon, hydrogen and oxygen atoms do not change Fusion reactions – multiple atomic particles join together to form a heavier nucleus: 12C + 1H→13N + γ (Energy)


Slide11: Nuclear fusion reactions can happen only under very high temperatures Energy released is ~1000000 times larger than in chemical reactions


Slide12: Proton-Proton chain


The Sun’s Energy Source is ThermonuclearFusion in its Core: The Sun’s Energy Source is Thermonuclear Fusion in its Core Proton-proton chain Four hydrogen nuclei “fuse” to form a single helium nucleus Thermonuclear fusion occurs only at the very high temperatures at the Sun’s core Will continue to heat the Sun for another 5 billion years


The Structure of the Sun: The Structure of the Sun The Interior Core (0.2 Solar radii) Radiative zone (0.2-0.7 Solar radii) Convection zone The Surface and Atmosphere Photosphere Chromosphere corona


Convection in the Solar Interior: Convection in the Solar Interior Below the visible surface of the Sun is a region known as the convection zone Here, turbulent convective motions occur, similar to a pot of boiling water. These bubbling motions are responsible for the granulation pattern seen on the Sun’s surface.


• 1000 km wide• occur in the Solar  Photosphere: • 1000 km wide • occur in the Solar Photosphere Solar Granulation


The Solar Atmosphere : The Solar Atmosphere The Sun’s atmosphere has three main layers: photosphere, chromosphere corona Everything below the solar atmosphere is called the solar interior The visible surface of the Sun, the photosphere, is the lowest layer in the solar atmosphere


Sunspots: Sunspots Regions of low temperature and intense magnetic fields Darkest part is called the “umbra” Just outside the umbra is the penumbra Sunspots are most-easily seen in the photosphere


The Corona: The Corona The outermost layer of the solar atmosphere, the corona, is made of very high-temperature gases at extremely low density What heats the corona remains an open question!


The Solar Constant: The Solar Constant Solar Luminosity Total energy emitted by the Sun per second L = 3.9 x 1026 W = 3.9 x 1026 Joules/sec One Joule is the work done, or energy expended, by a force of one Newton (N) moving an object one meter along the direction of the force The force of Earth’s gravity on the 220 pounds human is about 1000 N 1 Calorie (food energy, upper case C) = 4184 J 1 gram TNT (trinitrotoluene) = 4184 J


Slide21: Energy Conversion 2000 Calories. How many Joules? Suppose we use 2000 Calories per day. How many Watts we use? The biggest hydrogen bomb (Tsar Bomba) was ~100 Megatons of TNT (1 Megaton= 1012 grams) How many Tsar bombs would be necessary to explode per sec to maintain Solar Luminosity?


Energy Conversion: Energy Conversion 2000 Calories. How many Joules? 8.37 million Joules Suppose we use 2000 Calories per day. How many Watts we use? 96.8 Watts The biggest hydrogen bomb (Tsar Bomba) was ~100 Megatons of TNT How many Tsar bombs would be necessary to explode per sec to maintain Solar Luminosity? 3.9x1026 [J/sec]/(100x1012 [gTNT]*4184 [J/gTNT]) ~ 1 billion Tsar bombs per sec


Slide23: Why Earth is not destroyed by the Solar energy? Solar Flux Luminosity divided by the area (the amount of energy per sec per area) Solar Constant Solar Flux at the Earth’s orbit Rearth-orbit =1.5x108 km L/(4 x (Rearth-orbit)2) = ….


The solar constant: The solar constant


Go Solar?: Go Solar? The largest hydroelectric power station system (Canada) has max power production at ~ 16,000 MW Suppose we want to use the solar energy instead and generate similar power production. From what area do we need to collect the solar radiation?


But the Sun is not really constant !: But the Sun is not really constant ! Solar luminosity varies What causes this variability is an active area of research


Slide28: How does the Sun Influence Earth? Provides the energy that creates life, warms the planet, drives the dynamic atmosphere and oceans. UV light can cause mutations. Geomagnetic storms Aurora Power-grid failures (Canada, 1989); Telecommunications failures High-energy solar particles can destroy ozone lethal radiation dosages to astronauts and passengers/pilots on polar air-travel routes


Solar Evolution: Solar Evolution Earth will be likely destroyed Collapse of the hydrogen molecular cloud