Conceptual Questions 2 Flashcards
What is the main use of Newton’s version for Kepler’s 3rd Law:
P^2 = [4pi^2/G(m1 + m2)]a^3
The main use of Newton’s version is to determine the masses of celestial objects.
Orbital energy: EQ
for an elliptical orbit what happens when the planet is closest vs furthest from the star?
What trajectories arise from negative and positive values of E?
The planet’s orbital speed is slower the farther the planet is from the star. The planet’s orbital speed is faster the closer the planet is to the star.
the trajectory is hyperbolic when the total energy is positive.
The trajectory is elliptical when the total energy is negative.
Black Body Radiation:
How does the total energy radiated per unit area depend on the temperature?
The total energy radiated per unit area is directly proportional to the temperature. Therefore as temperature increases the total energy per unit area increases.
Black Body Radiation:
How does the peak of the emitted energy depend on the temperature?
As the temperature of the blackbody increaes the total energy radiated increases. The peak of the radiation curve wavelength will then shorten when energy increases.
Black Body Radiation:
The angular resolution of a telescope depends on what variables and in what way?
The angular resolution of a telescope (the smallest angle that can be resolved) is proportional to the
wavelength of the light and inversely proportional to the diameter of the mirror
Black Body Radiation:
The 4 fundamental stellar equations - what is the physical meaning of each side in each equation?
hydrostatic equilibrium - outward force due to pressure gradient within the star is balanced by the inward force due to gravity
conservation of mass - total mass before is equivalent to total mass after
thermal equilibrium - equality of internal energy, heat in is equivalent to heat out
radiative equilibrium - total radiation leaving object is equal to the total thermal radiation in
Spectral Line Formation:
What is the Saha equation?
Describes how the state of ionization of a particular element in a star changes with varying temperature and pressures.
Spectral Line Formation:
What is the Boltzmann Equation?
The equation shows what the distribution of the atoms will be among the various energy levels as a function of energy and temperature.
Spectral Line Formation:
How do boltzmann and saha equation together explain this plot?
spectral lines in stars are dictated by the population of atoms at different excitiation states (boltzmann distribution) and ionization fractions (saha eq). Both are related to temperature and pressure of star.
Spectral Line Formation:
And why is the temperature at the peak similar to the surface temperature of A stars?
assuming the star is a black body the tempearture at the peak is similar to the surface temperature.
Spectral Line Formation:
What are the two terms in the following equation?
Ptotal = row/mu mH KT + 1/3aT^4
Radiation pressure and density pressure
SLF:
Why does a neutrino emitted at the sun’s center take only 2.3 seconds to get out of the sun?
Neutrinos rarely interact with matter. Only a small amount of neutrinos produced are absorbed as they escape the sun.
SLF:
Why does a photon emitted at the sun’s center take many thousands of year to get out of the sun?
The sun’s density causes a photon emitted at the center to be absorbed by another proton. This absorption and re emission continuously happens.
SLF:
What is Thomson scattering and what is Thomson cross section?
A type of scattering of photons by free charged particles in which the outgoing photon has the same frequency/wavelength as the incoming photon.
The cross section is a scattering of photons when the energy of each individual is smaller than the rest energy of the electron.
SLF:
How does the sun produce its luminosity?
The sun converts hydrogen nuclei into a helium nucleus. This nuclear reactions generates energy and neutrinos.
