Astronomy Calculators
Absolute Magnitude Calculator
Calculate a star's absolute magnitude from its apparent magnitude and distance using the distance modulus formula.
Angular Size Calculator
Calculate the angular size of an astronomical object as seen from a given distance, from its true diameter.
Escape Velocity Calculator
Compute the exact escape velocity for Earth, the Moon, Mars, Jupiter, or a custom mass and radius using the standard gravitational escape velocity formula.
Habitable Zone Calculator
Estimate the habitable zone distance range around a star from its luminosity, the orbital range where liquid water could plausibly exist.
Hubble's Law Velocity Calculator
Calculate a galaxy's recession velocity from its distance using Hubble's Law, the foundational relationship describing the expanding universe.
Light Year Calculator
Convert light-years to kilometers, miles, astronomical units, or parsecs using exact speed-of-light and Julian-year constants for precise distances.
Moon Phase Calculator
Find the Moon's phase and approximate illumination percentage for any date, based on the 29.53059-day average synodic lunar month cycle length.
Orbital Period Calculator
Apply Kepler's third law to find orbital period from semi-major axis, using solar system units or general SI units for any two orbiting bodies in space.
Orbital Velocity Calculator
Determine the circular orbital velocity at any radius around Earth, the Moon, Mars, Jupiter, the Sun, or a custom central body mass in kilograms.
Parallax Distance Calculator
Calculate a star's distance in parsecs and light-years from its measured parallax angle in arcseconds.
Planet Weight Calculator
Calculate what you would weigh on any planet, the Moon, or the Sun by scaling your Earth weight with each body's published surface gravity ratio precisely.
Planetary Position Calculator
Estimate a planet's approximate orbital angle on any date using a circular-orbit mean-motion model anchored to the standard J2000.0 epoch reference date.
Redshift Velocity Calculator
Calculate an object's recession velocity from its measured redshift value using the simplified low-redshift approximation.
Roche Limit Calculator
Calculate the Roche limit distance at which tidal forces would tear apart a satellite orbiting a larger body.
Schwarzschild Radius Calculator
Calculate the Schwarzschild radius (event horizon size) for a given mass in solar masses.
Star Distance Calculator
Convert a star's measured parallax angle directly into distance in parsecs and light-years using the standard inverse-parallax distance formula astronomers rely on.
Stellar Luminosity Calculator
Calculate a star's luminosity relative to the Sun from its radius and surface temperature using the Stefan-Boltzmann Law.
Sunrise Sunset Calculator
Calculate precise sunrise, sunset, and total day length for any date and coordinates using solar declination and hour-angle astronomical formulas.
Synodic Period Calculator
Calculate the synodic period between two orbiting bodies from their individual orbital periods, the time between successive similar alignments.
Telescope Magnification Calculator
Determine telescope magnification from telescope and eyepiece focal length in millimeters, with reference figures for common eyepiece combinations.
The Scale of Everything Beyond Earth
Astronomy deals in numbers so large that ordinary units stop being useful — distances measured in light years, velocities measured in kilometers per second, masses measured relative to other planets. These ten calculators convert those astronomical scales into numbers you can actually compare and reason about.
Escape velocity — the speed needed to break free of a body's gravity entirely — depends on both mass and radius, which is why a more massive planet does not always have a proportionally higher escape velocity than a smaller, denser one. It is also exactly why Apollo missions could launch back off the Moon with a small ascent stage, while leaving Earth requires the enormous multi-stage rockets that dominate spaceflight. Try different bodies in the Escape Velocity Calculator.
Popular Astronomy Calculators
- Light Year Calculator — converts between light years and standard distance units; despite the word "year," it measures distance (roughly 9.46 trillion km), not time.
- Orbital Period Calculator — finds how long a body takes to complete one orbit from its orbital radius and central mass.
- Moon Phase Calculator — finds the Moon's phase on any given date.
Interested in the physics behind orbital mechanics? See the Physics Calculators, or check spacecraft-specific math in Aerospace Calculators.