© 2005 pearson education inc., publishing as addison-wesley absorption spectra light shines through...

© 2005 Pearson Education Inc., publishing as Addison-Wesley

Absorption Spectra

• Light shines through a gas, atoms will absorb those photons of specific wavelengths that match the atom’s electron energy levels.

• Spectrum is missing those wavelengths that were absorbed.

• We can determine which elements are present in an object by the emission & absorption lines in the spectrum.


QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

• Homework #3 Due Tomorrow at noon .

• New Homework posted tomorrow:

Read: Chapters 5: “Light” Reading.“Light” Reading.

Chapter 8: First 10 pages only.

Light&

Origin of the Solar System

• Midterm #1: 12 days - Feb 26.– Covers Chapters 1-5 & 8 (skip 6,7) .

– 6 problems, similar to homework

– Equations provided; no calculator


Telescope Observations ProjectTelescope Observations ProjectTwo Parts Two Parts

1. Make Telescope Observations of two objects

Suggestions: Saturn, Mars, Orion Nebula

Telescope Hours: Tue & Thu 7-8 pm, 7th floor of Campbell Hall

Sketch both objects on 1/2 sheet of paper. Note Date and Time.

2. Mark the position of Mars with a dot, at three times during the Semester, early, middle, late. (Use either map.) Note date of each observation.

Good Night to Use Telescope & Detect Mars . . .Good Night to Use Telescope & Detect Mars . . .




Totality: 7:00 - 7:50 pmTotality: 7:00 - 7:50 pm

5:435:43

10:5010:50

9:099:09

7:007:00

Wed,Wed,


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Last Time:Last Time:


What a Planet is made of

• Chemical Composition of Surface and Atmosphere ?

• Temperature

• Ices, liquids, gases?QuickTime™ and aTIFF (Uncompressed) decompressor


Artist’s rendering: Recently discovered “dwarf planet”, ErisEris.One of many icy objects larger than Pluto in the Kuiper Belt of the outer Solar System.

Last Time:Last Time: Spectra Tell us:Spectra Tell us:


Light as a WaveLight as a Wave

• f is frequency is wavelength

• For light: f = c

c = 300,000 km/s

• Our eyes recognize f (or ) as ccoolloorr .



Light as photons

Light as a particle

E = hfEach Photon Each Photon Has an EnergyHas an Energy:



Emission of Light by Atoms or Molecules


Atoms and MoleculesAtoms and Molecules have have

Distinct Energy LevelsDistinct Energy Levels

Excited atoms & moleculesExcited atoms & moleculeschange from high to low,change from high to low,

photons emittedphotons emitted


Emission Spectra

• Each type of atom or molecule has a unique set of electron energy levels.

• Each emits its own set of wavelengths of light.

• Unique Emission line spectrum for each atom

or molecule.


Absorption Spectra

• Light shines through a gas, atoms will absorb those photons of specific wavelengths that match the atom’s electron energy levels.

• Spectrum is missing those wavelengths that were absorbed.

• We can determine which elements are present in an object by the emission & absorption lines in the spectrum.


Warm, Solid Objects Glow by

Thermal Emission of Light



Cool Warmer Hot HotterCool Warmer Hot HotterRed & Faint White & BrightRed & Faint White & Bright


1. Warm objects emit Infrared light and radio waves1. Warm objects emit Infrared light and radio waves Examples: Warm embers of fire, electric stove.

2. Hotter objects emit more light energy per unit surface area (per second). (Energy increases as Temp4 )

3. Hotter objects emit bluer photons (with a higher average energy.)

average increases as 1/ T (using kelvin Temp scale)

“Thermal Emission” from Warm, Opaque Objects


Thermal Radiation

Hot: more BlueHot: more Blue

Cold: more RedCold: more Red


1. Hotter objects emit more light energy per unit surface area (per second). Energy emitted = 6x10-8 T4

(Joules per m2 per sec)

2. Hotter objects emit bluer photons (with a higher

average energy.) “Wien Law”

max = 2.9 x 106 / T (nm)

“Thermal Emission” from Opaque Objects


Spectrum from a Typical Planet, Comet, or Asteroid

Spectrum reveals:Spectrum reveals:1 Chemical Composition2 Temperature3 Velocity

Reflected visible light from SunReflected visible light from Sun Thermal Emission (IR)Thermal Emission (IR)

Absorption by moleculesAbsorption by moleculesin gases in atmospherein gases in atmosphere


The Doppler Effect

Waves emitted from an object moving towards you will have its wavelength shortened.

The Doppler EffectThe Doppler Effect




The Doppler Effect


The Doppler Effectwith Light

1. Light from an object moving towards you will have its wavelength shortened.

2. Light from an object moving away from you will have its wavelength lengthened.

3. Light emitted from an object moving perpendicular to your line-of-sight will not change its wavelength.

BLUESHIFTBLUESHIFT

REDSHIFTREDSHIFT


The Doppler Effect

velocity c

=

Change in WavelengthChange in Wavelength

WavelengthWavelength


Measuring the Doppler Effect

• Measure the Doppler shift of emission or absorption lines in the spectrum of a planet.

• Calculate the velocity of the object in the direction either towards or away from Earth.

velocity c

==


. Formation of the Solar SystemFormation of the Solar System

Chapter 8Chapter 8


Circular Orbits (elliptical, but nearly circles) All planets lie in one flat plane (the

Ecliptic).

They orbits & spin in same direction (counter clockwise)

Inner Planets: small, rocky Outer Planets: large, made of gas and ice

Overall Properties Overall Properties of our Solar of our Solar SystemSystem

How did our Solar System Form ? ? ?How did our Solar System Form ? ? ?


Interstellar Gas and Dust in

Dust and GasDust and GasIn In

InterstellarInterstellarClouds !Clouds !

Light absorbedLight absorbedfrom distant starsfrom distant starsalong mid-plane.along mid-plane.

our Milky Way GalaxyMilky Way Galaxy


The Dark Clouds in the Milky Way

Centaurus AHST

Milky Way


The Interstellar Medium(ISM)

Dust &Gas


Dark CloudsAssociated with dense gas is about 1% (by mass) of “rocky/icy” grains that could eventually make terrestrial planets.


Absorptionof Light by DustDust clouds: Opaque in visible (“Optical”) light. Lower opacity in infrared.Dust scatters visible light more efficiently than infrared ==> To Study the Milky Way Galaxy: use IR !

Visible Light Infrared Light


Gas Clouds containhydrogen, helium, carbon,nitrogen, oxygen

and complex molecules


Small Dust particle:Only a few thousand atoms

Dust is Made of Atoms


Interstellar Dust Grain:Interstellar Dust Grain:

C, O, Si, HC, O, Si, H220 ice, Si-O.0 ice, Si-O.

Large Dust Particle: 10,000’s of Atoms!


Stars are continuously forming in the galaxy.

Basic Observation


The Origin of the Solar System

• Four characteristics of our Solar System must be explained by a formation theory.

• What is the basic idea behind the theory?


The Orion Nebula

Infrared View Stars: Only 1 Million years old.Stars: Only 1 Million years old.


80% of young stars 80% of young stars have protoplanetaryhave protoplanetarydisks.disks.

Disk masses measured Disk masses measured from from Millimeter-wavelengthMillimeter-wavelengththermal emissionthermal emissionof dust.of dust.Planet - buildingPlanet - building

material is common.material is common.


Protoplanetary Disks…

Solar System size

Star and planet formation

Measured Sizes: 100-1000 AU

Masses: 10-3 – 10-1 Msun


Disk of dust around AU Microscopii


are needed to see this picture.AU MicroscopiiAU Microscopii


Artists Rendering of Young Star Forming,and protplanetary disk




Protoplanetary Disks of Gas & Dust

Theory ofPlanet Formation:

Dust collides, sticks

and grows pebbles/rocks Gravity helps attract

more rocks Gravity attracts gas

Formation of Planetary SystemsFormation of Planetary Systems

ObservationsObservations Thermal Emission (Infrared)

from Dust Thermal Emission ( = 1 mm)

from cold dust far from star.

Hubble Space Telescope

Pictures of protoplanetary disks.

MDISK = 10-100 MJUP

Disk Lifetime ~ 3 Myr

Observations Models of



Our theory must explain the data

1. Planets in orderly motions:

circular orbits, flat plane, orbit same direction.

There are two types of planets.– small, rocky terrestrial planets– large, hydrogen-rich Jovian planets

Asteroids & comets exist in certain regions of the Solar System

There are exceptions to these patterns.



Theory – our Solar System formed from a giant, swirling cloud of gas & dust.

Depends on two principles of Physics:• Law of Gravity:

gravitational attraction of gas and

• Conservation of angular momentumand on

•Basic chemistry


Gravitational Collapseof Original Cloud

• The solar nebula was initially somewhat spherical and a few light years in diameter.– very cold

– rotating slightly

• Gravity pulled the atoms and molecules together. • As the nebula shrank, gravity increased, causing collapse.• As the nebula “falls” inward, gravitational potential

energy is converted to heat.– Conservation of Energy

• As the nebula’s radius decreases, it rotates faster– Conservation of Angular Momentum


As the nebula collapses, it heats

up, spins faster, and flattens.


Collapse of the Solar Nebula


Building the PlanetsSo only rocks & metals condensed within 3.5 AU of the Sun… the snow line.Hydrogen compounds (ices) condensed beyond the frost line.


Building the Planets

• Each gas (Jovian) planet formed its own “miniature” solar nebula.

• Moons formed out of the disk.


Lecture8


Flattening of the Solar Nebula• As the nebula collapses, clumps of gas collide & merge.

• Their random velocities average out into the nebula’s direction of rotation.

• The spinning nebula assumes the shape of a disk.



accretion -- small grains stick to one another via electromagnetic force until they are massive enough to attract via gravity to form...


Orderly Motions in the Solar System

• The Sun formed in the very center of the nebula.– temperature & density were high enough for nuclear fusion reactions to

begin

• The planets formed in the rest of the disk.

• This would explain the following:– all planets lie along one plane (in the disk)

– all planets orbit in one direction (the spin direction of the disk)

– the Sun rotates in the same direction

– the planets would tend to rotate in this same direction

– most moons orbit in this direction

– most planetary orbits are near circular (collisions in the disk)


Observe Radio WavesObserve Radio Wavesto Search for Waterto Search for Water


HH22O O Production:Production:

Earth’sEarth’sOceanOceanevery every 24 min24 min

HH2200


All planetary systemsAll planetary systems

are like ourare like our

Solar System . . .Solar System . . .


Rotating Molecules Detected Rotating Molecules Detected by by

Emission of Radio WavesEmission of Radio Waves

Water in theInterstellarMedium.

CO

Neutral Carbon


The Solar Nebula

• The nebular theory holds that our Solar System formed out of a nebula which collapsed under its own gravity.

• observational evidence – We observe stars in the process of

forming today.

– The are always found within interstellar clouds of gas.

newly born stars in the Orion Nebula

solar nebula – name given to the cloud of gas from which our own Solar System formed


Seeing Through the Dark

Optical HST View


Ring of Dustaround Fomalhaut




More Support for the Nebular Theory• We have observed disks around other stars.

• These could be new planetary systems in formation.

Pictoris

AB Aurigae


9.3 Creating Two Types of Planets

• What key fact explains why there are two types of planet?

• Describe the basic steps by which the terrestrial planets formed.

• Describe the basic steps by which the Jovian planets formed.

Our goals for learning:


Building the PlanetsCondensation – elements & compounds began to condense (i.e. solidify) out of the nebula…. depending on temperature!



…and temperature in the Solar nebula depended on distance from the Sun!


Building the Planets…planetesimals which will:• combine near the Sun to form rocky planets• combine beyond the frostline to form icy planetesimals

which… • capture H/He far from Sun to form gas planets



solar wind --- charged particles streaming out from the Sun cleared away the leftover gas


9.4 Explaining Leftovers and Exceptions to the Rules

• What is the origin of asteroids and comets?

• What was the heavy bombardment?

• How do we explain the exceptions to the rules?

• How do we think that our Moon formed?

Our goals for learning:


Origin of the Asteroids• The Solar wind cleared the leftover gas, but not the leftover

planetesimals.

• Those leftover rocky planetesimals which did not accrete onto a planet are the present-day asteroids.

• Most inhabit the asteroid belt between Mars & Jupiter.– Jupiter’s gravity prevented a planet from forming there.


Origin of the Comets

• The leftover icy planetesimals are the present-day comets.

• Those which were located between the Jovian planets, if not captured, were gravitationally flung in all directions into the Oort cloud.

• Those beyond Neptune’s orbit remained in the ecliptic plane in what we call the Kuiper belt.

The nebular theory predicted the existence of the Kuiper belt 40 years before it was discovered!


Exceptions to the Rules

• There were many more leftover planetesimals than we see today.

• Most of them collided with the newly-formed planets & moons during the first few 108 years of the Solar System.

• We call this the heavy bombardment period.

So how does the nebular theory deal with exceptions, i.e. data which do not fit the model’s predictions?


Exceptions to the Rules

• Why some moons orbit opposite their planet’s rotation– captured moons (e.g. Triton)

• Why rotation axes of some planets are tilted– impacts “knock them over” (extreme example: Uranus)

• Why some planets rotate more quickly than others– impacts “spin them up”

• Why Earth is the only terrestrial planet with a large Moon– giant impact

Close encounters with and impacts by planetesimals could explain:


Formation of the Moon(Giant Impact Theory)

• The Earth was struck by a Mars-sized planetesimal

• A part of Earth’s mantle was ejected

• This coalesced in the Moon.– it orbits in same direction as

Earth rotates

– lower density than Earth

– Earth was “spun up”

© 2005 pearson education inc., publishing as addison-wesley absorption spectra light shines through...

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