Astronomy & Astrophysics / Subcategory
Stellar Physics
Stellar physics calculators and formulas for radiation from stars and cosmic expansion. Includes luminosity, the Stefan-Boltzmann law, and Hubble's law calculations.
22Formulas
All levels Difficulty
Updated Oct 2026
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Fundamental
Cosmological Redshift to Recession Velocity
v ≈ c * z
Fundamental
Barlow Lens Combined Focal Length
f_new = f_telescope * Barlow_factor
Fundamental
Telescope Limiting Magnitude
m_lim ≈ 2.7 + 5*log10(D)
Fundamental
Angular Diameter of the Moon or Sun
θ = 2 * arctan(R / d)
Fundamental
Age of the Universe (Hubble Time, Approx.)
t_H ≈ 1 / H_0
Fundamental
Light Travel Time
t = d / c
Fundamental
Inverse Square Law of Flux (Brightness-Distance)
F = L / (4π d²)
Fundamental
Wien's Displacement Law
λ_max = b / T
Fundamental
Doppler Redshift (Radial Velocity)
v = c * (λ_observed - λ_rest) / λ_rest
Fundamental
Astrophotography NPF Rule (Simplified)
t_max = (35 * f_number + 30 * pixel_pitch) / focal_length
Fundamental
Astrophotography 500 Rule
t_max = 500 / (focal_length * crop_factor)
Fundamental
Telescope Exit Pupil
E = D / M
Fundamental
Telescope True Field of View
TFOV = AFOV / M
Fundamental
Telescope Focal Ratio (f-number)
f/# = f / D
Fundamental
Telescope Resolving Power (Dawes' Limit)
R = 116 / D
Fundamental
Telescope Magnification
M = f_telescope / f_eyepiece
Fundamental
Small-Angle Formula (Angular Size)
θ (arcsec) = 206265 * (d / D)
Fundamental
Distance Modulus
m - M = 5*log10(d) - 5
Fundamental
Parallax Distance (Parsec)
d = 1 / p
Fundamental
Moon Illumination Fraction
k = (1 + cos(θ)) / 2
Fundamental
Hubble's Law
v = H₀d
Fundamental
Stefan-Boltzmann Law (Luminosity)
L = 4πR²σT⁴