Introduction to Astrophysics/Laws and Formulae
Gravitation edit
Kepler's Laws edit
- The orbit of each planet is an ellipse which has the sun at one of its foci.
- Each planet moves in such a way that the line joining it to the sun sweeps out equal areas in equal times.
- The squares of the periods of revolution of the planets about the Sun are proportional to the cubes of their mean distance from it.
Newton's gravitational law edit
F = | The gravitational force between two bodies. |
G = | Universal gravity constant, 6.67 x 10^{−11} N m^{2} kg^{−2} |
m_{1} = | The mass of the first body. |
m_{2} = | The mass of the second body. |
r = | The distance between the centres of mass of two bodies. |
Black body radiation edit
Wein’s displacement law(only for black bodies)
λ_{max} = W/T
Wein’s constant(W)= 2.90 × 10^{−3} m K
T= temperature of the black body
Stefan's Law edit
E = | Rate of energy radiated from the surface of a black body per unit area. |
σ = | Stefan's constant, 5.67 × 10^{−8} W m^{−2} K^{−4} |
T = | Surface temperature of the black body. |
Stellar Magnitude edit
Apparent Magnitude edit
m = | Apparent magnitude of star. |
I = | Intensity of light received. |
K = | a constant |
Pogson's Formula edit
m_{1} = | Apparent magnitude of first star. |
m_{2} = | Apparent magnitude of second star. |
I_{1} = | Intensity of light received from first star. |
I_{2} = | Intensity of light received from second star. |
Absolute Magnitude edit
m = | Apparent magnitude of star. |
M = | Absolute magnitude of star. |
d = | Distance to star in parsecs. |