Comet Shoemaker-LevyComet Shoemaker-Levy

Bit of Administration ….Bit of Administration ….• ReadingReading

– BSNV Chaps. 9 and 15 BSNV Chaps. 9 and 15

• Additional observations for Lab 2, through April 5Additional observations for Lab 2, through April 5

– Due April 7 in lecture or April 9 at Mathieu officeDue April 7 in lecture or April 9 at Mathieu office

• 12-week exam in two weeks - April 12, 7:15 pm, 3425 Sterling12-week exam in two weeks - April 12, 7:15 pm, 3425 Sterling

– Review session, Sunday, April 11, Review session, Sunday, April 11, 7:30 pm, 7:30 pm, 3425 Sterling3425 Sterling

NOTE CHANGE NOTE CHANGE

IN TIME!IN TIME!

The Formation of the Solar SystemThe Formation of the Solar System

• Dense Molecular CoresDense Molecular Cores (“Bok Globules”)(“Bok Globules”)

• ≈ ≈ 1 M1 Moo

• ≈ ≈ 50,000 AU50,000 AU• ≈ ≈ 10 10 ooKK

The Formation of the Solar SystemThe Formation of the Solar System

The Formation of the Solar SystemThe Formation of the Solar System• Grain Grain CollisionsCollisions ==> Planetesimals (100 km) ==> Planetesimals (100 km) randomrandom

100 km100 km

The Formation of the Solar SystemThe Formation of the Solar System

• Planetesimal Planetesimal AccretionAccretion ==> Rocky Planets and Jovian Cores ==> Rocky Planets and Jovian Cores gravitygravity

The Formation of the Solar SystemThe Formation of the Solar System

• Gas Gas AccumulationAccumulation ==> H and He onto Jovian Cores ==> H and He onto Jovian Cores gravitygravity

ProtomoonsProtomoons

The Formation of the Solar SystemThe Formation of the Solar System

The Formation of the Solar SystemThe Formation of the Solar System

• Dispersal of Hydrogen and Helium GasDispersal of Hydrogen and Helium Gas• Solar Wind?Solar Wind?• Jets?Jets?

Most comets have orbits that take them well beyond Jupiter. You Most comets have orbits that take them well beyond Jupiter. You would expect their composition to be: would expect their composition to be:

A) Rocks and heavy elements onlyA) Rocks and heavy elements only B) Rocks and ices onlyB) Rocks and ices only C) Rocks, ices, and hydrogen and heliumC) Rocks, ices, and hydrogen and helium

ConcepTest!ConcepTest!

The SunThe Sun

QuickTime™ and aYUV420 codec decompressorare needed to see this picture.

The SunThe Sun

The Sun is the source of (almost) all energyThe Sun is the source of (almost) all energyin the Solar Systemin the Solar System

How does it work?How does it work?

The SunThe SunI. Hydrostatic Equilibrium - “on average, nothing moves”I. Hydrostatic Equilibrium - “on average, nothing moves”

• Gravity always acts to collapse the SunGravity always acts to collapse the Sun• Gas pressure acts against collapseGas pressure acts against collapse

Gravity

PressurePressureP = n k TP = n k T

€

Fg =GM1M2

R2

NumberNumberDensityDensity

(Particles(Particlesper cmper cm33))

TemperatureTemperature(( o oK )K )

BoltzmannBoltzmannconstantconstant

The SunThe Sun

I. Hydrostatic EquilibriumI. Hydrostatic Equilibrium• Higher central pressure is required to hold up greater weightHigher central pressure is required to hold up greater weight

Gravity

PressurePressureP = n k TP = n k T

€

Fg =GM1M2

R2 Central Temp = 15 million Central Temp = 15 million ooKKCentral Density = 150 gm/cmCentral Density = 150 gm/cm33

The SunThe Sun

High Temperatures at Center of SunHigh Temperatures at Center of Sunhave nothing to do withhave nothing to do with

Nuclear Energy!Nuclear Energy!

Required Pressure SupportRequired Pressure Supportagainst Gravity producesagainst Gravity produces

High Temperatures at Center of SunHigh Temperatures at Center of Sun

The atmosphere of the Earth is in hydrostatic equilibrium. This The atmosphere of the Earth is in hydrostatic equilibrium. This explains why explains why

A) Air gets colder as you climb mountains.A) Air gets colder as you climb mountains. B) Air gets “thinner” as you climb mountains.B) Air gets “thinner” as you climb mountains. C) Both A and BC) Both A and B

ConcepTest!ConcepTest!

The SunThe Sun

II. Energy FlowII. Energy Flow

Radius0 1 Ro

Tem

pera

ture

o K

0

107

Energy flow

Hot

“Cool”

The SunThe Sun

The Sun does NOT ShineThe Sun does NOT Shinebecause ofbecause of

Nuclear Energy!Nuclear Energy!

The Sun ShinesThe Sun Shinesbecause it isbecause it is

Hotter in CenterHotter in Centerthan Surfacethan Surface

The SunThe SunII. Energy Flow - MechanismsII. Energy Flow - Mechanisms

QuickTime™ and aYUV420 codec decompressorare needed to see this picture.

The SunThe Sun

II. Energy Equilibrium - “Energy emitted = Energy produced”II. Energy Equilibrium - “Energy emitted = Energy produced”

What are energy sources for Sun’s luminosity?What are energy sources for Sun’s luminosity?

1.1. GravityGravitya)a) Energy emitted at surfaceEnergy emitted at surfaceb)b) Core cools downCore cools downc)c) Central pressure goes downCentral pressure goes downd)d) Sun contractsSun contractse)e) Core heats upCore heats upf)f) Central pressure goes upCentral pressure goes upg)g) Energy emitted at surface ……Energy emitted at surface ……

Energy emitted at surface <==> Star contractsEnergy emitted at surface <==> Star contracts

The SunThe Sun

II. Energy Equilibrium - “Energy lost = Energy produced”II. Energy Equilibrium - “Energy lost = Energy produced”

What are energy sources for Sun’s luminosity?What are energy sources for Sun’s luminosity?

1.1. GravityGravity

Net Effect = Energy emitted at surface and star contractsNet Effect = Energy emitted at surface and star contracts

Kelvin-Helmholtz Timescale = Time for Sun => R = 0Kelvin-Helmholtz Timescale = Time for Sun => R = 0 = 10 million years= 10 million years

But Earth is 4.5 billion years old,But Earth is 4.5 billion years old, So must be another source of energy ….So must be another source of energy ….

The SunThe SunII. Energy Equilibrium - “Energy lost = Energy produced”II. Energy Equilibrium - “Energy lost = Energy produced”

What are energy sources for Sun’s luminosity?What are energy sources for Sun’s luminosity?

1.1. GravityGravity2.2. NuclearNuclear

E = MC2

EnergyEnergy(joules)(joules) MassMass

(kg)(kg)

Speed of lightSpeed of light(3 x 10(3 x 1088 m/sec) m/sec)

The SunThe Sun

Thermonuclear Hydrogen Fusion 4 H => HeThermonuclear Hydrogen Fusion 4 H => He

4 H = 4 x 1.673 x 104 H = 4 x 1.673 x 10-27-27 kg = 6.693 x 10 kg = 6.693 x 10-27-27 kg kg- 1 He = 6.645 x 10- 1 He = 6.645 x 10-27-27 kg kg__________________________________________________________________________________ 0.048 x 100.048 x 10-27-27 kg kg

(0.048 x 10(0.048 x 10-27-27 kg) * (3 x 10 kg) * (3 x 1088 m/s) m/s)22 = 4.3 x 10 = 4.3 x 10-12-12 joules joules

6 x 106 x 101414 kg H => He per second in the Sun! kg H => He per second in the Sun!

The SunThe Sun

Thermonuclear Hydrogen Fusion 4 H => HeThermonuclear Hydrogen Fusion 4 H => He

Why “Thermonuclear”?Bringing two positive charges together

Requires high velocity = high temperature

Positron

Neutrino

Deuterium

Hydrogen

Helium 4

Helium 3

Closing ThoughtClosing Thought

• The Second Law of ThermodynamicsThe Second Law of Thermodynamics

Heat can never pass spontaneously from a colderHeat can never pass spontaneously from a colderto a hotter body. to a hotter body.

As a result of this fact, As a result of this fact, naturalprocesses that involve energy transfer naturalprocesses that involve energy transfer

must have one direction, must have one direction, and all natural processes are and all natural processes are

irreversible.irreversible.