< Introduction to Astrophysics
Gravitation
Kepler's Laws
- 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
F = | The gravitational force between two bodies. |
G = | Universal gravity constant, 6.67 x 10−11 N m2 kg−2 |
m1 = | The mass of the first body. |
m2 = | The mass of the second body. |
r = | The distance between the centres of mass of two bodies. |
Black body radiation
temperature of the black body.
- w = 2.90 × 10−3 m K
Stefan's Law
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
Apparent Magnitude
m = | Apparent magnitude of star. |
I = | Intensity of light received. |
K = | a constant |
Pogson's Formula
m1 = | Apparent magnitude of first star. |
m2 = | Apparent magnitude of second star. |
I1 = | Intensity of light received from first star. |
I2 = | Intensity of light received from second star. |
Absolute Magnitude
m = | Apparent magnitude of star. |
M = | Absolute magnitude of star. |
d = | Distance to star in parsecs. |
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