# Astrophysics Reference Formulas

If you entered the website here, welcome! Whilst there are many online resources that might seem that they provide similar information, the driver for astrophysicsformulas.com can be summarized by the phrases *practical and quickly accessible* and *time-saving convenience*. The astrophysics reference list of astronomy formulas and astrophysics formulas is given below, in alphabetical order. To find what you are looking for if you can’t find it in the list, either search this webpage (e.g., using “apple-F” on a mac) or search the website using the search box in the right-hand sidebar.

We also have a free pdf download that you can take away. It is actually 50 pages long and presents a concise list of common astrophysics formulas that we hope will serve as a useful off-line reference. However, note that the website is currently lagging behind the pdf file in the number of entries, but the website entries have more extensive explanations than the pdf file entries, often with examples. Please come back soon and/or sign-up in the right-hand sidebar for e-mail updates. The pdf file download page can be accessed by the link or button above.

### A

Angular Distance Between Two Points on a Sphere

Apparent Magnitude and Absolute Magnitude Scale

### B

### C

### D

Distance versus Redshift for $z\ll 1$

Doppler Broadening Thermal Line Width

Doppler Shift for Light and Radiation

### E

Eddington Luminosity

Escape velocity

Event Horizon of a Black Hole

### F

Fine Structure Constant

FWHM Gaussian FWHM Calculation

### G

GeV to kg Conversion

Gravitational Radius

### I

### K

Kelvin to keV Conversion

keV to Kelvin Conversion

Kepler’s Laws

kg to eV Conversion

kg to GeV Conversion

kg to MeV Conversion

### L

Light-Crossing Times

Lorentz Transformations in Special Relativity

Lorentzian FWHM Calculation

### M

Maxwell’s Equations

Maxwell-Boltzman velocity distribution

MeV to kg Conversion

### O

Orbital Velocity (various useful forms)

Orbital Period

### P

Parallax – Definition of Parallax

### R

Rayleigh-Jeans Law (Low frequency limit for blackbody)

Reduced Mass

Root Mean Square Velocity of Particles in a Gas with Maxwellian Velocity Distribution

### S

Schwarzschild Radius

Solid Angle Definition

Stefan-Boltzmann (flux versus temperature for a blackbody)

### W

Wien Displacement Law

Wien’s Law Spectrum (high-frequency limit of blackbody spectrum)