MT 1
TRUE/FALSE: Green light has longer wavelength than red light.
How is energy related to wavelength? Frequency?
False
E is proportional to frequency and inversely proportional to wavelength
How does a main-sequence star's luminosity scale with mass?
How about Radius?
True/False: If you double the mass of a white-dwarf, its luminosity increases by a factor of 16
L is proportional to M^4
R is proportional to M
Trick question! Above relationships only hold for main-sequence stars
How do you resolve Olbers' paradox?
Universe has a finite age
Where is the center of the universe?
Nowhere and everywhere
(in an inaccessible dimension)
What material are the inner planets made of? Outer planets?
Mercury, Venus, Earth, Mars: rocky planets with heavy elements (came from supernovae!)
Jupiter,Saturn,Uranus,Neptune: Gas giants - mostly Hydrogen and Helium
What observations suggest the presence of "dark matter"?
Galaxy rotation curves
Gravitational lensing due to galaxy clusters
What is the cosmological principle?
Universe is isotropic and homogeneous on large scales
What are the three possibilities for a universe if cosmological constant is zero?
Open, Flat, Closed
Discuss the properties
What time does the North Pole star set in December, as seen from California?
It doesn't! Trick question :)
What are the evolutionary stages of a 3 solar mass main-sequence star?
Main-sequence -> Red giant -> planetary nebula -> White dwarf -> (possible type Ia SN if WD exceeds 1.4 solar masses)
TRUE/FALSE: If there is no cosmological constant, a universe with any amount of matter must be decelerating
TRUE
What is the maximum age of a universe which is always decelerating?
1/Hubble constant
You want to build a telescope. What problems should you be aware of?
Spherical aberration for reflecting telescopes
Chromatic aberration for refracting telescopes
Effect of atmosphere
larger telescope - larger collecting area (so can see fainter objects)
Resolution
If you spot a white dwarf and a red giant in a binary orbit, which one was more massive when it was a main-sequence star?
White dwarf: because it evolved faster. Remember more massive stars evolve quicker
Draw a timeline of the universe until recombination
Planck time -> 10^-43 s (quantum fluctuations)
inflation -> 10^-37 to 10^-35 (GUT force breaks)
particle-antiparticle equilibrium broken -> 10^-35 to 10^-6
nucleosynthesis -> 10 s - 10 minutes
recombination -> 380,000 years
Why were only H, He and some Li formed during the big bang nucleosynthesis?
Need a narrow temperature range for fusion to occur.
If too hot, protons bounce-off after collision
If too cold, not enough energy to overcome electric repulsion
What are some methods of detecting exoplanets?
Transit: when a planet crosses in front of a star (most common method)
Doppler Wobble: periodic red and blue shift due to planet tugging on the star (can determine minimum mass of planet)
Direct imaging: least successful so far
How do we determine Hubble's constant?
Is is really a constant?
Measure recession velocities of galaxies from redshift observed in spectra
Measure distances using Cepheid variables (relatively nearby galaxies) and/or Tyoe Ia supernovae (really far away galaxies)
No Hubble's constant changes with time!
What is Heisenberg's Uncertainty Principle?
Cannot measure both position and momentum simultaneously with high precision
Cannot measure both energy and time interval simultaneously with high precision
How is it possible to do interstellar travel within a human lifetime?
Special relativity: travel at a significant fraction of speed of light
Time dilates, lengths contract