Astronomy Formulas
Astronomy and astrophysics formulas for orbital mechanics, Kepler's laws, stellar luminosity, redshift, and cosmological distance.
Angular Size Formula
Calculate the angular size of any object using its physical size and distance. Includes the small angle approximation and examples with planets and the Moon.
Stellar Magnitude Formula (Pogson Scale)
The stellar magnitude formula explained — apparent magnitude, absolute magnitude, and the Pogson scale. Includes worked examples with real stars.
Luminosity Distance Formula
Calculate stellar luminosity distance using the inverse square law from absolute and apparent magnitudes or observed flux. Covers parsecs, light-years, and Mpc.
Tidal Force Formula
Reference for the tidal force differential gravity formula. Explains ocean tides, the Roche limit, and tidal locking with examples for planetary systems.
Drake Equation
Reference for the Drake equation: N = R* x fp x ne x fl x fi x fc x L. Estimate detectable civilizations in the Milky Way by adjusting each factor.
Escape Velocity Formula
Calculate the minimum speed needed to escape a planet or star's gravitational pull. Essential for space travel calculations.
Hubble's Law
Hubble's law (v=H0*d) relates a galaxy's recession velocity to its distance. The foundation of the expanding universe model and Big Bang cosmology.
Kepler's Third Law
Kepler's third law relates a planet's orbital period to its distance from the star. Calculate orbits for any celestial body.
Orbital Velocity Formula
Reference for orbital velocity v = sqrt(GM/r). Calculate the speed for a stable circular orbit around Earth or Moon from orbital radius and central mass.
Parallax Distance Formula
Calculate distance to nearby stars using stellar parallax. Enter parallax angle in arcseconds to get distance in parsecs and light-years with a worked example.
Schwarzschild Radius
Reference for Schwarzschild radius r_s = 2GM/c² for black hole event horizons. Returns r_s for the Sun, Earth, and supermassive black holes in meters.
Stellar Luminosity Formula
Calculate a star's total energy output using the Stefan-Boltzmann law L = 4piR^2 * sigma * T^4. Relates luminosity to stellar radius and surface temperature.