Astronomy Calculators
Free astronomy calculators for planets, stars, and cosmic distances — explore the universe from your browser. No signup required.
See your weight on all 8 planets, the Moon and Pluto at once.
Find out how old you would be if you lived on another planet.
Convert light years to km, AU and parsecs with cosmic comparisons.
Find the moon phase for any date and see the next full and new moon.
Calculate the escape velocity for any planet or custom body.
Find the event horizon radius of any mass.
Apply Kepler's third law to find the orbital period of any body.
Convert between absolute and apparent magnitude using the distance modulus.
Calculate recession velocity from redshift using Hubble's law.
Find the angular size of any object at any distance.
Distinguish between sidereal and synodic orbital periods.
Estimate your sky quality and what you can observe from your location.
About these astronomy calculators
These astronomy tools put cosmic scales in human terms. Find how your weight changes as surface gravity varies across the planets — from the crushing pull of Jupiter to the gentle tug of Mars. Convert vast distances between light years, astronomical units, and parsecs with context about what each unit represents in practice.
Every tool runs entirely in your browser with no signup required. Whether you're a student exploring orbital mechanics, an amateur astronomer planning a night's observation, or simply curious about the universe — these calculators are ready immediately.