Astronomy Calculators

Telescope Exit Pupil Calculator

Calculate exit pupil, magnification, and limiting magnitude for any telescope and eyepiece. Find the best eyepiece for planetary or deep-sky observing.

CCD Pixel Scale Calculator for Astrophotography

Calculate pixel scale in arcsec/pixel from camera pixel size and telescope focal length. Includes oversampling check and field of view per frame.

Drake Equation Calculator

Estimate the number of communicative civilizations in the Milky Way using the Drake equation. Adjust the seven factors and explore SETI scenarios.

Eddington Luminosity Calculator

Calculate the Eddington luminosity limit for a stellar or compact object from its mass. Used in stellar physics, black hole accretion, and X-ray binaries.

Hill Sphere Radius Calculator

Calculate the Hill sphere radius — the gravitational influence zone where a body can hold satellites against the parent star or planet.

Planet Equilibrium Temperature Calculator

Estimate the equilibrium temperature of a planet from stellar luminosity, distance, and bond albedo. Used in exoplanet habitability and climate studies.

Tidal Locking Time Calculator

Estimate how long it takes a satellite or planet to become tidally locked to its primary using the standard Q-rigidity formula. Used in exoplanet habitability.

Absolute Magnitude Calculator

Calculate a star's absolute magnitude from apparent magnitude and distance, or find distance from magnitudes. Includes distance modulus.

Age of the Universe from Hubble Constant

Estimate the age of the universe from the Hubble constant. Calculate Hubble time and ΛCDM-corrected age. Compare to the accepted value of 13.8 billion years.

Angular Diameter Calculator

Calculate the angular diameter of any astronomical object from its physical size and distance. Returns results in degrees, arcminutes, and arcseconds.

Apparent Magnitude vs Distance Calculator

Calculate apparent magnitude change with distance using the inverse-square law and distance modulus. Returns star brightness at any new distance.

Asteroid Impact Energy Calculator

Calculate the kinetic energy of a meteor or asteroid impact in megatons of TNT. Enter size, density, and impact speed; compare results to Tunguska and Chicxulub.

Binary Star Total Mass Calculator

Calculate the total mass of a binary star system using Kepler's third law from orbital period and semi-major axis. Optionally find individual masses.

Chandrasekhar Limit — White Dwarf Mass Calculator

Calculate the Chandrasekhar mass limit for white dwarfs using electron degeneracy pressure. Understand why this limit triggers Type Ia supernovae.

Einstein Ring Angular Radius Calculator

Calculate the Einstein ring radius for gravitational lensing. Enter lens mass and distances to find the angular radius in arcseconds.

Exoplanet Transit Depth Calculator

Calculate the transit depth in flux and ppm when an exoplanet crosses its star. Find transit duration from orbital parameters.

Galaxy Recession Speed and Lookback Time

Calculate how fast a galaxy is receding and estimate its lookback time from its distance. Includes superluminal recession check.

Gravitational Time Dilation Calculator

Calculate how much slower time passes in a gravitational field. From GPS satellites to black hole event horizons — general relativity in action.

Hawking Radiation Temperature Calculator

Calculate the Hawking radiation temperature of a black hole and its evaporation timescale. Lighter black holes are hotter and evaporate faster.

Hubble's Law Recession Velocity Calculator

Calculate galaxy recession speed using Hubble's Law. Choose from Planck 2018, standard, or local H₀ values. Includes Hubble sphere check.

Interstellar Travel Time Calculator

Calculate travel time to nearby stars at any fraction of light speed. Includes relativistic proper time for the traveler and time dilation factor.

Julian Date Converter

Convert any calendar date to Julian Date (JD) and Modified Julian Date (MJD). Also convert JD back to calendar date. Essential for astronomy.

Magnitude to Brightness Ratio Calculator

Convert between stellar magnitudes and brightness ratios. Find out how many times brighter or dimmer one star is compared to another.

Main Sequence Star Lifetime Calculator

Estimate how long a star spends on the main sequence based on its mass. Uses the mass-luminosity relation to calculate stellar lifetime.

Moon Phase Calculator

Calculate the Moon phase for any date. Find moon age in days, phase name, and illumination percentage. Based on the synodic month of 29.53 days.

Neutron Star Density Calculator

Calculate the average density, surface gravity, and escape velocity of a neutron star from its mass and radius. Compare to nuclear density.

Orbital Period Calculator (Kepler's Third Law)

Calculate orbital period from semi-major axis using Kepler's third law. Supports the Sun, Earth, Jupiter, or any custom central body.

Planetary Escape Velocity Calculator

Calculate the escape velocity of any planet, moon, or body. Compare to Earth's 11.2 km/s. Supports built-in presets and custom mass and radius.

Planetary Surface Gravity Calculator

Calculate surface gravity on any planet, moon, or body. Find the weight of a 70 kg person in Newtons and Earth-equivalent kilograms.

Redshift and Recession Velocity Calculator

Calculate galaxy recession velocity from redshift z, or find z from rest and observed wavelengths. Includes relativistic formula and Hubble distance.

Roche Limit Calculator

Calculate the Roche limit — the distance inside which a satellite breaks apart due to tidal forces. Explains planetary rings and comet disruption.

Satellite Orbital Period Calculator

Calculate orbital period and speed for Earth satellites. Enter altitude and get period in minutes, velocity in km/s, and orbit classification (LEO/MEO/GEO/HEO).

Schwarzschild Radius (Black Hole) Calculator

Calculate Schwarzschild radius in meters and km using r_s = 2GM/c². Returns event horizon for Earth (9 mm), the Sun (3 km), and supermassive black holes.

Signal / Light Travel Time Calculator

Calculate light or signal travel time for any distance in space. Returns time in seconds to years — Moon (1.3 sec), Sun (8.3 min), nearest star (4.2 years).

Solar Flux at Distance Calculator

Calculate the solar irradiance at any distance from the Sun. Compare to Earth's solar constant of 1,361 W/m². Includes planet presets.

Solar Noon Time Calculator

Calculate approximate solar noon (local apparent noon) for any longitude and date. Includes equation of time correction and UTC offset.

Star Color and Temperature Calculator

Find a star's peak wavelength and color from its temperature using Wien's law, or estimate temperature from the B-V color index. Includes spectral class.

Stellar Habitable Zone Calculator

Calculate the inner and outer edges of a star's habitable zone — where liquid water can exist on a planet's surface. Enter luminosity or radius and temperature.

Stellar Luminosity Calculator

Calculate a star's luminosity from its radius and surface temperature using the Stefan-Boltzmann law. Results in watts and solar luminosities.

Stellar Mass-Luminosity Relation Calculator

Calculate a main-sequence star's luminosity from its mass using the empirical mass-luminosity relation. Includes spectral class and lifetime estimate.

Stellar Parallax Distance Calculator

Calculate stellar distance from parallax angle in arcseconds using d(pc) = 1/p. Returns distance in parsecs, light-years, and AU — used by Hipparcos and Gaia.

Stellar Radial Velocity (Doppler Spectroscopy) Calculator

Calculate a star's radial velocity from observed spectral line shift. Determine if a star is approaching (blueshift) or receding (redshift).

Synodic Period Calculator

Calculate a planet's synodic period — the time between successive oppositions or conjunctions as seen from Earth. Select any planet or enter a custom period.

Telescope Angular Resolution Calculator

Calculate a telescope's angular resolution limit using the Rayleigh criterion and Dawes limit. Find what you can resolve on the Moon, planets, and beyond.

Tidal Force Calculator

Calculate the tidal force and tidal acceleration exerted by a massive body across an extended object. Understand tides, Roche limits, and spaghettification.

Transit Probability Calculator

Calculate the geometric probability that an exoplanet will transit its host star as seen from Earth. Shows why nearby stars are best targets.

Vis-Viva Equation — Orbital Speed Calculator

Calculate orbital velocity at any point using the vis-viva equation v^2=GM(2/r-1/a). Find speeds at periapsis, apoapsis, and circular orbit for comparison.

Delta-V Budget Calculator

Calculate fuel mass and mass ratio for rocket missions using the Tsiolkovsky equation. Enter delta-v, exhaust velocity, and dry mass for total fuel required.

Newtonian Telescope Collimation Calculator

Calculate the secondary mirror offset for a Newtonian reflector telescope to achieve correct collimation. Ensure accurate optical alignment for sharp views.

Orbital Velocity Calculator

Calculate orbital velocity in km/s for a satellite above Earth, Mars, or the Moon. Returns orbital period and comparison to the ISS at 408 km altitude.

Star Magnitude Calculator

Calculate the brightness ratio between stars using Pogson's magnitude scale. Enter two apparent magnitudes to find how many times brighter one star is.

Telescope Field of View Calculator

Calculate true and apparent field of view for any telescope and eyepiece. Enter focal length and aperture to find magnification, exit pupil, and sky coverage.

Telescope Limiting Magnitude Calculator

Calculate the limiting magnitude (faintest visible star) for any telescope aperture. An 8-inch scope reaches mag 13.1. Compare refractors, reflectors, and SCTs.

Telescope Magnification Calculator

Calculate telescope magnification, field of view, and exit pupil from focal lengths. Find the best eyepiece for your telescope.

Light Year Distance Calculator

Convert astronomical distances between light-years, km, miles, AU, and parsecs. Includes travel time at various speeds and known star distances for scale.

Weight on Other Planets Calculator

Calculate your weight in lbs and kg on every planet, the Moon, and the Sun from surface gravity. Returns weight and gravity multiplier for all 8 planets.