lecture3 - ECE2984 Lecture3 SPACEENVIRONMENT:THESUN...

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ECE 2984 cture 3 Lecture 3 SPACE ENVIRONMENT: THE SUN Joseph Baker (ECE Dept) Lecture 3: The Sun ECE 2984:Exploration of Space
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The Sun he un ntains 9 f e tal ass f e lar stem The Sun contains 99.8% of the total mass of the solar system. The Sun is a “normal” G2 star, one of more than 100 billion stars in our galaxy. The Sun is in the top 10% of stars in the galaxy by mass. The median size of stars in our galaxy is less than half the mass of the Sun. At present, the Sun is about 75% hydrogen and 25% helium by mass. This will change slowly over time as the Sun converts hydrogen to helium in its core. he un bout illion ars ld nd alf ay rough s resent hase The Sun is about 4.5 billion years old and half way through its present phase. Eventually it will run out of hydrogen fuel and expand to engulf the Earth. Joseph Baker (ECE Dept) Lecture 3: The Sun ECE 2984:Exploration of Space
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The Sun as a Star Joseph Baker (ECE Dept) Lecture 3: The Sun ECE 2984:Exploration of Space Herzsprung Russell diagram
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Solar Properties Distance from the Earth 1.496x10 8 km 2.35x10 4 R E Mass 1.99x10 31 kg 333,000 M E Radius 6.96x10 5 km 109 R E Mean density 1.91 g cm 3 Density in the center 98 g cm 3 rface gravity 74 m s 2 Surface gravity 274 m s Escape velocity 618 km s 1 Luminosity 3.86x10 23 kW 1366.1 Wm 2 @ Earth Rotation 26 days (equator) 36 days (poles) Surface Temperature 5778 K (Assuming Stefan Boltzmann Law q= σ T 4 ) ass Loss rate 0 g s Joseph Baker (ECE Dept) Lecture 3: The Sun ECE 2984:Exploration of Space Mass Loss rate 10 9 Kg s 1
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Fusion Reaction The sun is a fusion reactor: 4 H 1 Î He 4 + 26.73 MeV D = Deuteron γ = gamma ray ν = neutrino e + = positron e = electron OTE he diation kes NOTE: The radiation takes 10 million years to diffuse outward and reach the rface Joseph Baker (ECE Dept) Lecture 3: The Sun ECE 2984:Exploration of Space surface
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Stefan Boltzmann Law q = σ T 4 Joseph Baker (ECE Dept) Lecture 3: The Sun ECE 2984:Exploration of Space
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Blackbody spectrum Joseph Baker (ECE Dept) Lecture 3: The Sun ECE 2984:Exploration of Space
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Solar Radiation (a) X RAYS AND EXTREME ULTRAVIOLET (EUV) ( λ <1800 Å) contributes about 10 3 of total energy output. Emitted from lower corona and chromosphere and varies during the solar cycle with enhancements up to an order of magnitude during flares. (b) ULTRAVIOLET (1800Å < λ < 3500Å) contributes about 9% of solar flux. Radiated from photosphere and corona – varies during solar cycle. ) ISIBLE 500 500 ) ntributes bout 0 f lar ux nd (c) VISIBLE (2500Å < λ < 3500Å) contributes about 40% of solar flux and does not vary substantially with solar cycle. Emitted from photosphere. (d) INFRARED (7400Å < λ <10 7 Å) has maximum energy flux of 51% with no substantial variation during solar cycle. Emitted from photosphere. (e) RADIO ( λ > 1mm) originates from corona and contributes only about 10 10 %ofsolarflux ‐‐ can be enhanced significantly during solar flares.
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lecture3 - ECE2984 Lecture3 SPACEENVIRONMENT:THESUN...

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