Astronomy 7 Midterm #2 Review

I wasn't in class on May 18^th... the cold fusion part, so you'll have to look in your own notes for that.

Relativity (I'll explain this in detail since it's kinda confusing)

• Galilean Relativity

  • velocities of objects add: this is the relativity we are used to

  • If I travel at 20 miles/hr, and a train is coming towards me at 20 miles/hr, I would see the train pass me at (20 + 20) = 40 miles/hr

• Special Relativity

  • at high velocity, v close to c, the speed of light, one needs the concept of inertial frames to discuss time and position

  • c, the speed of light, is 300,000 km/s, and it is always CONSTANT, no matter what velocity the observer is traveling at

    • even if you are traveling at 99% the speed of light, you light a candle, and the light from the candle will radiate away from you at c, 300,000 km/s

  • this introduces time dilation and length contraction

    • time dilation: to a stationary observer, the time of a moving observer appears to slow down

      • t_observer = t_mover * gamma

    • length contraction: to a stationary observer, the length of an object is longer than it appears to a moving observer

      • L_observer = L_mover/gamma

• "gamma" = 1/ (1-v²/c²)^1/2

• General Relativity

  • the theoretical basis: inertial mass is equal to gravitational mass

  • this means: accelerating frame is equal to gravitational frame

  • therefore, light is bent by a mass, or, mass distorts space-time so that a light ray traveling by will be bent

  • GR. has definite predictions which have been confirmed

    • precession of Mercury's orbit

      • due to the Sun's presence, space time around the sun is distorted, and the orbit of Mercury will be slightly "off", meaning after one revolution, it won't return to exactly the same place. This has been measured

    • deflection of starlight by the sun

      • due to the Sun's presence, starlight directly behind the sun will be deflected into view. This has been measured during a solar eclipse.

    • gravitational lenses

      • due to the presence of intervening mass, much like the deflection of starlight by the sun, background objects can be lensed by foreground objects, and either be, a) strong lensing: produce multiple images or b) weak lensing: produce brightening of image. Both cases have been observed and confirmed to following GR.

Black Holes

• know what a black hole is

  • a clump of matter where the density is so great, no known force can hold it up and it collapses to a singularity.

• know the different types of black holes

  • primordial black holes, stellar black holes, galactic black holes

  • they basically differ by the amount of mass they contain

• know the formation process of a stellar sized black hole

• know the definitions of: escape velocity, event horizon, Shwarzschild radius, singularity, gravitational redshift, potential well.

• know how to calculate tidal forces

  • the difference in gravitational force between your head and your toe

  • tidal forces near solar mass black holes are so large, they will stretch you as thin as atoms

• know what an accretion disk is

  • it emits a lot of radiation, and a black hole accretion disk can be one of the brightest things in the sky

• weird black hole stuff

  • theoretically, things called "wormholes" can connect between black holes as rips in space

  • if you run time backwards, you can get stuff like white holes, the opposite of black holes, where they constantly spew out stuff

Cosmology

• The study of the whole universe on the largest scales

• know what cosmology tries to answer

  • what is the universe? how old is the universe? how was the universe created?

• know Olber's Paradox

  • why is the sky dark at night if the universe is infinite and has been around forever?

• know the solution to the paradox

• know the Hubble parameter and how we measure it

• know what critical density means

  • rho_critical = 3H²/8piG

  • omega = rho/rho_critical

• know the three possible geometries of the universe is (see section notes week6 for brief rundown)

• know the connection between the Hubble parameter and the age of the universe

• know the what a "standard candle" is and how it's used in measuring Hubble's parameter

• know the timeline of the universe

  • nucleosynthesis, last scattering, galaxy formation, present time

• know what a reshift is

  • z = delta_lambda/lambda, where lambda is the wavelength of the light we are measuring

• know what the CMB is

  • Comic Microwave Background, photons from the surface of Last Scattering

  • occured at z = 1100, when the universe was about 3500 kelvin

• know the dark matter problem

  • "missing mass" detected from galactic rotation curves

  • know the candidates for dark matter

    • MACHOs and WIMPs

Cold Fusion

• know what fusion and fission is

• know why fusion is such an attractive idea

  • solves energy problem

• know the two types of fusion (hot and cold) and what the difference is

• know the four basic forces

  • electromagnetic, gravity, strong nuclear, weak nuclear

• know two ways of containing a fusion reaction