SMALL QUESTIONS. COSMIC PERSPECTIVES.

A wider universe.
A clearer calculation.

From starlight and orbital motion to your telescope. Explore 30 free astronomy calculators, with units, formulas and assumptions in view.

30 focused calculatorsNo sign-upDefinitions, clearly explained

ASTRONOMY

One au. 499 light-seconds.

30 FOCUSED TOOLSONE CLEAR RESULT ↗

English interface · Local calculations · No sign-up.

DISTANCESDisplay currency

Astronomical distance converter

Method & assumptions

YOUR ASTRONOMY TOOLKIT

Find your next calculation.

30 calculators, together on one page.

Interactive calculators require JavaScript. Available tools:

Astronomical distance converter — Convert metres, kilometres, au, light-years and parsecs.

Light travel time — Find one-way travel time in vacuum.

Parallax distance — Estimate parsec distance from stellar parallax.

Distance from modulus — Infer distance from apparent and absolute magnitudes.

Absolute magnitude — Correct apparent magnitude for distance and extinction.

Apparent magnitude — Predict apparent magnitude at a specified distance.

Brightness ratio from magnitudes — Compare two fluxes in the same band.

Magnitude difference from flux — Convert a positive flux ratio into m1−m2.

Blackbody stellar luminosity — Estimate bolometric luminosity from radius and temperature.

Flux from luminosity — Apply inverse-square dilution to an isotropic source.

Blackbody peak wavelength — Find the peak of the wavelength-form blackbody spectrum.

Photon energy — Convert vacuum wavelength into photon energy.

Frequency from wavelength — Convert vacuum wavelength to frequency.

Spectral redshift — Compare observed and rest-frame wavelengths.

Relativistic radial Doppler speed — Map a pure radial special-relativistic redshift to speed.

Low-redshift Hubble distance — Estimate distance with a user-selected Hubble constant.

Kepler orbital period — Calculate period in a two-body test-particle model.

Circular orbital speed — Find speed at a circular orbital radius.

Escape speed — Find local Newtonian escape speed.

Surface gravitational acceleration — Calculate acceleration outside a spherical body.

Schwarzschild radius — Calculate the event-horizon radius for a non-rotating black hole.

Telescope magnification — Compare telescope and eyepiece focal lengths.

Telescope focal ratio — Find focal length divided by aperture.

Exit pupil — Estimate the visual exit-pupil diameter.

Diffraction resolution — Estimate a circular aperture’s Rayleigh angular resolution.

Approximate true field of view — Estimate field from eyepiece apparent field and magnification.

Camera image scale — Estimate angle per pixel at telescope focus.

Angular diameter — Find exact angular size for a transverse flat diameter.

Angular separation on the sky — Find great-circle separation of two equatorial directions.

Altitude from hour angle — Convert declination and local hour angle to altitude.

01 / FOCUSED

Thirty distinct tools.

Each calculator has its own inputs, definition and worked example.

02 / TRANSPARENT

Know the method.

See the formula and domain restrictions next to the result. Precision and assumptions are explained.

03 / LOCAL

Your inputs stay in your browser.

Calculations run locally. Advertising and hosting practices are described separately in the privacy page.