Donaldson R F Free Space and Astronomy Tools
Calculators and references for orbits, planets, stars, telescopes and the night sky.
22 free tools in this category. No sign-up, no limits.
Planet Facts Table
Compare the Sun's planets, Pluto and the Moon: mass, size, gravity, distance, orbit, temperature and more, side by side.
Open tool →Planet Weight Calculator
See what you would weigh on the Moon, Mars, Jupiter and every other planet, worked out from each one's own surface gravity.
Open tool →Age on Other Planets
Find out how old you would be in Mercury years, Mars years, Jupiter years and more, based on each planet's real orbital period.
Open tool →Light Travel Time Calculator
Work out how long light takes to cross a distance in km, million km, AU or light-years, or pick a planet to see its light delay from the Sun.
Open tool →Julian Date Converter
Convert between a calendar date, the astronomical Julian Date, the Modified Julian Date (MJD) and a Unix timestamp.
Open tool →Astronomical Distance Converter
Convert between kilometres, astronomical units (AU), light-years and parsecs, the everyday units used for distances in space.
Open tool →Kepler's Third Law Calculator
Work out an orbit's period, semi-major axis or the central body's mass from Kepler's third law, in AU, years and solar masses.
Open tool →Orbital & Escape Velocity Calculator
Work out the circular orbital speed and escape velocity at any height above a planet, moon or your own custom body.
Open tool →Mars Sol Converter
Convert between Earth days and Mars sols (Martian solar days), the unit NASA's rover missions use, with the Mars24 conversion factor.
Open tool →Sunrise & Sunset Calculator
Find sunrise, solar noon, sunset and civil, nautical and astronomical twilight for any date and place, using NOAA's public solar-position formulas.
Open tool →Sidereal Time Calculator (GMST & LST)
Work out Greenwich Mean Sidereal Time (GMST) and Local Sidereal Time (LST) for any UTC date, time and longitude, using the IAU 1982 formula.
Open tool →Rocket Equation Calculator
Work out delta-v, mass ratio, propellant mass or final mass with the Tsiolkovsky rocket equation, from specific impulse and rocket mass.
Open tool →Hohmann Transfer Delta-v Calculator
Work out the two burns, total delta-v and transfer time for a Hohmann transfer between two circular orbits around a planet, moon or custom body.
Open tool →Star Luminosity, Radius & Temperature Calculator
Work out a star's luminosity, radius or surface temperature from the other two, using the Stefan-Boltzmann law, plus its Wien's law peak wavelength.
Open tool →Stellar Magnitude & Distance Calculator
Work out a star's distance, absolute magnitude or apparent magnitude using the distance modulus, from parsecs or a parallax in arcseconds.
Open tool →Redshift & Doppler Velocity Calculator
Convert between spectroscopic redshift (z), wavelength shift and radial velocity, with both the classical (v = cz) and exact relativistic Doppler formula.
Open tool →Exoplanet Equilibrium Temperature Calculator
Work out a planet's equilibrium temperature from its star's temperature and radius, the orbital distance and the planet's Bond albedo.
Open tool →Geostationary Dish Look Angle Calculator
Work out the elevation and azimuth (compass bearing) to point a dish at a geostationary satellite, from your latitude, longitude and the satellite's orbital longitude.
Open tool →Habitable Zone Calculator
Work out a star's conservative and optimistic habitable zone boundaries in AU, from its temperature and luminosity, using the Kopparapu et al. (2013) model.
Open tool →Transit Depth & Duration Calculator
Work out an exoplanet transit's depth and duration from the planet and star's radii, the orbital period, semi-major axis and impact parameter.
Open tool →Asteroid Diameter from Magnitude Calculator
Estimate an asteroid's diameter from its absolute magnitude (H) and an assumed albedo, using NASA/JPL's own asteroid size estimation formula.
Open tool →Impact Energy & Crater Calculator
Estimate an asteroid or meteor impact's kinetic energy and resulting crater size, from its diameter, density, speed and impact angle.
Open tool →