© 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.

© 2005 Pearson Education Inc., publishing as Addison-Wesley Homework #3 Due Tomorrow at noon. New Homework posted tomorrow: “Light” Reading. Read: Chapters 5: “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

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

© 2005 Pearson Education Inc., publishing as Addison-Wesley Totality: 7:00 - 7:50 pm 5:43 10:50 9:09 7:00 Wed,

© 2005 Pearson Education Inc., publishing as Addison-Wesley Light Last Time:

© 2005 Pearson Education Inc., publishing as Addison-Wesley What a Planet is made of Chemical Composition of Surface and Atmosphere ? Temperature Ices, liquids, gases? Eris Artist’s rendering: Recently discovered “dwarf planet”, Eris. One of many icy objects larger than Pluto in the Kuiper Belt of the outer Solar System. Last Time: Spectra Tell us:

© 2005 Pearson Education Inc., publishing as Addison-Wesley Light as a Wave f is frequency  is wavelength For light: f = c c = 300,000 km/s colorOur eyes recognize f (or ) as color. Last Time:

© 2005 Pearson Education Inc., publishing as Addison-Wesley Light as photons Light as a particle E = hf Each Photon Has an Energy Has an Energy: Last Time:

© 2005 Pearson Education Inc., publishing as Addison-Wesley Emission of Light by Atoms or Molecules Last Time: Atoms and Molecules have have Distinct Energy Levels Excited atoms & molecules change from high to low, photons emitted

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

© 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.

© 2005 Pearson Education Inc., publishing as Addison-Wesley Warm, Solid Objects Glow by Thermal Emission of Light Cool Warmer Hot Hotter Cool Warmer Hot Hotter Red & Faint White & Bright

© 2005 Pearson Education Inc., publishing as Addison-Wesley 1. 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 Temp 4 ) 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

© 2005 Pearson Education Inc., publishing as Addison-Wesley Thermal Radiation Hot: more Blue Cold: more Red

© 2005 Pearson Education Inc., publishing as Addison-Wesley 1. 1.Hotter objects emit more light energy per unit surface area (per second). Energy emitted = 6x10 -8 T 4 (Joules per m 2 per sec) 2. 2.Hotter objects emit bluer photons (with a higher average energy.) “Wien Law” max = 2.9 x 10 6 / T (nm) “Thermal Emission” from Opaque Objects

© 2005 Pearson Education Inc., publishing as Addison-Wesley Spectrum from a Typical Planet, Comet, or Asteroid Spectrum reveals: Spectrum reveals: 1Chemical Composition 2Temperature 3Velocity Reflected visible light from Sun Thermal Emission (IR) Absorption by molecules in gases in atmosphere

© 2005 Pearson Education Inc., publishing as Addison-Wesley The Doppler Effect Waves emitted from an object moving towards you will have its wavelength shortened. The Doppler Effect

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

© 2005 Pearson Education Inc., publishing as Addison-Wesley The Doppler Effect with Light 1. 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. BLUESHIFT REDSHIFT

© 2005 Pearson Education Inc., publishing as Addison-Wesley The Doppler Effect  velocity c = Change in Wavelength Wavelength

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

© 2005 Pearson Education Inc., publishing as Addison-Wesley Formation of the Solar System. Formation of the Solar System Chapter 8

© 2005 Pearson Education Inc., publishing as Addison-Wesley 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 of our Solar System How did our Solar System Form ? ? ?

© 2005 Pearson Education Inc., publishing as Addison-Wesley Interstellar Gas and Dust in Dust and Gas InInterstellar Clouds ! Light absorbed from distant stars along mid-plane. Milky Way Galaxy our Milky Way Galaxy

© 2005 Pearson Education Inc., publishing as Addison-Wesley The Dark Clouds in the Milky Way Centaurus A HST Milky Way

© 2005 Pearson Education Inc., publishing as Addison-Wesley The Interstellar Medium (ISM) Dust & Gas

© 2005 Pearson Education Inc., publishing as Addison-Wesley Dark Clouds Associated with dense gas is about 1% (by mass) of “rocky/icy” grains that could eventually make terrestrial planets.

© 2005 Pearson Education Inc., publishing as Addison-Wesley Absorption of Light by Dust Dust 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

© 2005 Pearson Education Inc., publishing as Addison-Wesley Gas Clouds contain hydrogen, helium, carbon,nitrogen, oxygen and complex molecules

© 2005 Pearson Education Inc., publishing as Addison-Wesley Small Dust particle: Only a few thousand atoms Dust is Made of Atoms

© 2005 Pearson Education Inc., publishing as Addison-Wesley Interstellar Dust Grain: C, O, Si, H 2 0 ice, Si-O. Large Dust Particle: 10,000’s of Atoms!

© 2005 Pearson Education Inc., publishing as Addison-Wesley Stars are continuously forming in the galaxy. Basic Observation

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

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

The Orion Nebula Infrared View Stars: Only 1 Million years old.

© 2005 Pearson Education Inc., publishing as Addison-Wesley 80% of young stars have protoplanetary disks. Disk masses measured from Millimeter-wavelength thermal emission of dust. Planet - building material is common.

© 2005 Pearson Education Inc., publishing as Addison-Wesley Protoplanetary Disks… Solar System size Star and planet formation Measured Sizes: AU Masses: – M sun

© 2005 Pearson Education Inc., publishing as Addison-Wesley Disk of dust around AU Microscopii AU Microscopii

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

Artists Rendering of Young Star Forming, and protplanetary disk

© 2005 Pearson Education Inc., publishing as Addison-Wesley Protoplanetary Disks of Gas & Dust Theory of Planet Formation: Dust collides, sticks and grows  pebbles/rocks Gravity helps attract more rocks Gravity attracts gas Formation of Planetary Systems Observations Thermal Emission (Infrared) from Dust Thermal Emission ( = 1 mm) from cold dust far from star. Hubble Space Telescope Pictures of protoplanetary disks.  M DISK = M JUP Disk Lifetime ~ 3 Myr Observations  Models of

© 2005 Pearson Education Inc., publishing as Addison-Wesley Origin of the Solar System 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.

© 2005 Pearson Education Inc., publishing as Addison-Wesley Origin of the Solar System 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 momentum and on Basic chemistry

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

© 2005 Pearson Education Inc., publishing as Addison-Wesley As the nebula collapses, it heats up, spins faster, and flattens.

© 2005 Pearson Education Inc., publishing as Addison-Wesley Collapse of the Solar Nebula

© 2005 Pearson Education Inc., publishing as Addison-Wesley Building the Planets So only rocks & metals condensed within 3.5 AU of the Sun… the snow line. Hydrogen compounds (ices) condensed beyond the frost line.

© 2005 Pearson Education Inc., publishing as Addison-Wesley Building the Planets Each gas (Jovian) planet formed its own “miniature” solar nebula. Moons formed out of the disk.

© 2005 Pearson Education Inc., publishing as Addison-Wesley Lecture8

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

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.

© 2005 Pearson Education Inc., publishing as Addison-Wesley Building the Planets accretion -- small grains stick to one another via electromagnetic force until they are massive enough to attract via gravity to form...

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

© 2005 Pearson Education Inc., publishing as Addison-Wesley Observe Radio Waves to Search for Water

© 2005 Pearson Education Inc., publishing as Addison-Wesley H 2 O Production:Earth’sOceanevery 24 min H20H20H20H20

© 2005 Pearson Education Inc., publishing as Addison-Wesley All planetary systems are like our Solar System...

© 2005 Pearson Education Inc., publishing as Addison-Wesley Rotating Molecules Detected by Emission of Radio Waves Water in the Interstellar Medium. CO Neutral Carbon

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

© 2005 Pearson Education Inc., publishing as Addison-Wesley Seeing Through the Dark Optical HST View

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

Ring of Dust around Fomalhaut

© 2005 Pearson Education Inc., publishing as Addison-Wesley More Support for the Nebular Theory We have observed disks around other stars. These could be new planetary systems in formation.  Pictoris AB Aurigae

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

© 2005 Pearson Education Inc., publishing as Addison-Wesley Building the Planets Condensation – elements & compounds began to condense (i.e. solidify) out of the nebula…. depending on temperature!

© 2005 Pearson Education Inc., publishing as Addison-Wesley Building the Planets …and temperature in the Solar nebula depended on distance from the Sun!

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

© 2005 Pearson Education Inc., publishing as Addison-Wesley Building the Planets solar wind --- charged particles streaming out from the Sun cleared away the leftover gas

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

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

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

© 2005 Pearson Education Inc., publishing as Addison-Wesley 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 10 8 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?

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

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