Astronomy
Light Year Converter
Convert light years to kilometres, miles, astronomical units and parsecs — and back again.
1 light year = 9.4607 × 10¹² km = 63,241 …
Also called light years to km · light year to miles
Science · 11 calculators
Astronomy Calculators
Light-years, AU and parsecs, orbital periods, escape velocity, surface gravity, weight on other planets and telescopes.
Astronomy
Astronomical Unit Converter
Convert astronomical units to km, miles, light minutes and light years — the scale of the solar system.
1 AU = 149,597,870.7 km = the average Ear…
Also called au to km · astronomical unit to miles
Astronomy
Parsec Converter
Convert parsecs to light years, AU and kilometres, and find the parallax angle that defines them.
1 pc = 3.2616 light years = 206,265 AU
Also called parsec to light years · pc to ly
Astronomy
Orbital Period Calculator
Orbital period and speed from the semi-major axis using Kepler's third law, for any central mass.
T = 2π√(a³ / GM)
Also called kepler third law · orbit time calculator
Astronomy
Escape Velocity Calculator
Speed needed to escape a planet or star’s gravity, for the solar system bodies or a custom mass.
v_esc = √(2GM / r)
Also called escape speed · how fast to leave earth
Astronomy
Surface Gravity Calculator
Surface gravity of a planet or moon in m/s² and g, with the weight of an object there.
g = GM / r²
Also called gravity on other planets · g force planet
Astronomy
Weight on Other Planets Calculator
What you would weigh on every planet, the Moon and the Sun — your mass never changes, only the pull.
weight = mass × local gravity
Also called weight on mars · weight on the moon
Astronomy
Telescope Magnification Calculator
Magnification, exit pupil and useful limits for a telescope and eyepiece combination.
Magnification = telescope focal length ÷ …
Also called eyepiece magnification · telescope power
Astronomy
Focal Ratio Calculator
Focal ratio (f-number) of a telescope or lens from focal length and aperture, with exposure impact.
f-ratio = focal length ÷ aperture
Also called f number calculator · f ratio telescope
Astronomy
Angular Size Calculator
Apparent angular size of an object from its real size and distance, in degrees, arcminutes and arcseconds.
θ = 2·arctan(size / 2d)
Also called apparent size · angular diameter
Astronomy
Distance Modulus Calculator
Convert between distance and the distance modulus using apparent and absolute magnitude.
m − M = 5·log₁₀(d) − 5, d in parsecs
Also called apparent magnitude · absolute magnitude
Key astronomy formulas
| Light Year Converter | 1 light year = 9.4607 × 10¹² km = 63,241 AU = 0.3066 pc |
|---|---|
| Astronomical Unit Converter | 1 AU = 149,597,870.7 km = the average Earth–Sun distance |
| Parsec Converter | 1 pc = 3.2616 light years = 206,265 AU · distance (pc) = 1 / parallax (arcsec) |
| Orbital Period | T = 2π√(a³ / GM) · Kepler: T² ∝ a³ |
| Escape Velocity | v_esc = √(2GM / r) |
| Surface Gravity | g = GM / r² |
| Weight on Other Planets | weight = mass × local gravity |
| Telescope Magnification | Magnification = telescope focal length ÷ eyepiece focal length |
| Focal Ratio | f-ratio = focal length ÷ aperture |
| Angular Size | θ = 2·arctan(size / 2d) |
Astronomy questions
How long is a light year in years?
It is not a time at all — it is the distance light covers in a year, about 9.46 trillion km.