ASTR 1514 1st EditionExam # 2 Study Guide o How a collapsing molecular cloud becomes a hot proto-star- It’s important to note that this process is NOT catastrophic, it just requires a lot of time. - Molecular clouds start off cold- Denser regions within the cloud collapse due to self-gravity- When particles have self-gravity they exert gravitational attractions to each other which leads to a net gravitational force toward the center of the cloud. - This gravitational energy becomes energy of motion as the particles move, or fall in toward the center, during their movement the energy of motion is convertedto Heat Energy, due to the particles colliding, similar to the process of friction.- Pressure on the inside of the cloud must equal the pressure outside, or the cloud will collapse- During the collapse, particles are then pulled toward the center heating the core ofthe cloud tremendously to form a dense proto-star. o Proto-star energy and luminosity- Proto-stars are large, cool, luminous, and emit infra-red lightThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Heat energy of proto-star transforms into light energy, known as Black Body Radiation. - Wien’s Law: A hotter black-body peaks at a shorter wavelength. Higher energy makes the light from the star bluer. - Stefan-Boltzmann Law: A hotter black-body is more luminous, Higher energy makes the star hotter and more luminous. o Angular Momentum- The rotation of a body, it’s the product of its moment of inertia and its angular velocity- Newton’s first law, all objects in motion stay in motion unless acted upon a force, can be applied to rotating objects, and the force acted up on it is the torque- Relationships of Angular Momentum 1. More Massive rotating body = more angular momentum2. Spinning faster = more angular momentum3. Larger radial extension = more angular momentum- Example of Conservation of angular momentum: A skater brings her arms inward and she spins faster, as the radial extent of her arms decrease s=that angular momentum is still on her rotating body, so it must be compensated for by her spinning faster. o There is not enough torque to slow down a molecular cloudo As a molecular cloud is collapse, it must spin faster in order to conserve angular momentum. o A cloud forms a proto-star at the center and a disk of dust and gas extended outward.o The proto-star and disk have conserved angular momentum, the star is small but massive, however the disk is extended. o Extrasolar Planetso 1889 Extrasolar planets have been confirmed, first one discovered in 1995. o The different ways for finding extra-solar planets1. Direct imaging – Difficult because planets are small and faint2. Transit Method – Watch a star and look for dips in its overall brightness, each dip will occur at approximately same time so you can determine the orbital period. This process can take a long time3. Radial Velocity Method – Planet has a gravitational influence on parent star, both orbit about the center of mass. Farther distance from the center of Mass then the orbital period takes longer. More massive the object then the closer the center of mass is to that object. 4. Doppler Shifts – The motion of a light source toward or away from us changesthe wavelength of waves reaching us. Red-shift = away = lower frequency = longer wavelength. Blue-shift = toward = higher frequency = shorter wavelength.5. Gravitational Lensing. Easier to find a planet closer to a star, because the dip in the total brightness decreases more, or the gravitational influence is greater making it more noticeable. o Terrestrial Worlds: Earth, Venus, Earth’s moon. Mars, and Mercury. o Earth’s moon formed due to a collision of early molten Earth and a Mars sized proto-planet. Earth’s crust is similar to the composition of the Moon. o Number of craters on a body indicates the surfaces age: (More craters means an older surface with minimal geological activity.)o Radiometric Datingo Determine the age of a rock by finding how much of a radioactive material remains in an element compared with how many it started with. o Using Half-Lives (the time it takes for half of the sample to decay)o Potassium 40 decays into Argon 40 with a half-life of 1.25 billion years. o The fraction of potassium 40 that has turned into Argon 40 gives the age of the rock. o Magnetic Fieldso Earth’s magnetic field is produced by the different rotation rates of the Solid Innercore and Liquid outer core.o Earth and Mercury are the only planets with substantial magnetic fieldso Formation of Planets from proto-planetary Disko Within the disk, particles are moving along together in orbit around the staro Particles stick together to form larger particles, those larger particles sweep up smaller particles that get in the wayo Gravity also draws smaller particles onto larger particleso Planetesimals – Larger aggregates more than 1 kilometer acrosso Composition of Planetso Refractory Materials – Capable of withstanding high temperatures without melting or being vaporized. Ex: Iron and Silicates, this is why the terrestrial planets are made of refractory materials, because they are close to the sun withoutvaporizing. Earth, Mars, Venus, Mercury are made principally of refractory matertials. o Refractory materials condense at all radio Volatile Materials – Are in solid form only at very low temperatures, Ex: Water, ammonia, methane. Volatile material are in gas form when close to the star and escape. Jupiter, Saturn, Neptune, Uranus are principally made of Volatile Material. o Tectonismo Deformation of Earth’s crusto Earth’s lithosphere broken into plates that move, this described by continental drift o Crustal plates move due to convection. o Continental plates are made of low density rock so they float on top of the mantle and asthenosphere.o Earth has 7 major plates, o Sea- Floor Spreadingo Two plates separate and new lithosphere is created at the boundary, gives evidence to change in Earth’s magnetic field direction. o Plate collisiono Contitnetal plates float on the mantle where they collide to form mountainso Ex: Indian plate collides with Eurasian plate to form the Himalya mountains. o Subductiono Occurs when dense sea floor crust sinks under less dense continental crust. o Ex: Coast of Oregon/Washingtono Continental plates may pull apart and form a Rift, Ex: The Great