Astro Flashcards
(19 cards)
What’s the equation for the diameter of an object in terms of its angular diameter?
D = d*theta
What is the angular diameter?
The angle that is subtenden to from the observer’s position.
Equation for Luminosity
L = 4pid^2F
Definitions for luminosity and flux
Luminosity is an absolute measure of radiated electromagnetic energy per unit time; flux is the energy received per unit area per unit time.
Give Stegan’s Law
E = Stefan’s constant*T^4 (E is energy radiated per unit area per unit area; T is temp in kelvin)
What is blackbody radiation?
The thermal rad emitted by an idealilsed object that absorbs all light, with its spectrum depending only on temp - so no reflected light.
Give Planck’s Law
B_v = (2h_barfreq^3)/c^2 * 1/(e^(h_barfreq/kT)-1) - B_v is the spectral radience (power per unit area per unit wavelength per unit solid angle)
Give Wien’s Displacement Law
lambda_peak = b/T (b is the displacement constant)
What is the purpose of the Hydrostatic Equilibrium equation?
It balances pressure and gravity.
What is the purpose of the Mass Continuity equation?
Links density distribution to its mass profile
What is the purpose of the Energy Generation equation?
Used for modelling energy flow in regions like the Sun’s radiative zone.
What is the purpose of the Convective Transport equation?
Descibes temperautre gradient in regions where convection occurs, assuming abiatatic conditions. Used when the radiative gradient exceeds the adiabatic gradient.
What are the boundary equations for the stellar structure equations?
At center (r=0, M_r = 0): No mass enclosed at center, and no luminosity at center, as energy production starts slightly away from the center.
At surface (r=R or M_r =M): P=0, as no overlying matter; T=T_eff, related to effective temp (defined by star’s total lum and radius via the Stefan-Boltz law)
What’s the equation to estimate the temperture, as well as the assumption you make to use it?
T = GMmewm_H/5Rk (where mew is the mean molecular weight, and m_H is the mass of hydrogen). Assumption is uniform density.
What’s the equation to estimate the pressure, as well as the assumption you make to use it?
P =3GM^2/8piR^4. Assumptions are spherical symmetry and uniform density.
What’s the equation to estimate the thermal energy?
E_thermal = 3/10 * GM^2/R
What’s the equation to estimate the work done, as well as the assumption you make to use it? As well as the reason it’s negative
W = -3/5 * GM^2/R. Assumption is a sphere of uniform density, and it’s negative as it’s the binding energy.
Explain what the dynamical time is, and give the equation
It’s the time for object to collapse under gravity without pressure support. t_H = sqrt(3pi/32GP)
