Mar_4 - Planets Tuesday, March 4 Tue, Mar 4: Planets...

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Planets Planets Tuesday, March 4 Tuesday, March 4
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Tue, Mar 4: Planets Problem Set #7 due Problem Set #7 returned Tue, Mar 11, 1:30 pm 1:30 pm Final Exam Final Exam Comprehensive Same format as midterm
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What is a planet? Examples of planets:
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What is a planet? A ball of gas, liquid, and/or solid, orbiting a star, whose size is neither too big nor too small for a planet.
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Planets are smaller than stars. Within the Solar System, the mass of the Sun is 1000 × the mass of Jupiter .
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How small can a ball of gas be and still qualify as a star star ? A star has nuclear fusion nuclear fusion occurring in its interior. Fusion of hydrogen to helium requires T > 10 million Kelvin.
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A star is in hydrostatic hydrostatic equilibrium equilibrium . The smaller smaller a ball of gas, the lower lower the central pressure and temperature needed for hydrostatic equilibrium. If star’s mass < 0.08 Sun’s mass, central temperature < 10 million K.
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A ball of gas with less than 8% the Sun’s mass is not not a star. It is what astronomers call a brown dwarf brown dwarf .
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Brown dwarf = “failed star”. Like a star, it is a ball of gas. Like a star, it radiates light. Unlike a star, it doesn’t have a fusion “engine”, so it cools down. SUN
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Mar_4 - Planets Tuesday, March 4 Tue, Mar 4: Planets...

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