Astronomy Tools & Calculators
CosmoToolbox gathers 20 free astronomy tools and calculators for observing the night sky and exploring the physics of the cosmos. Track the ISS, convert Julian dates, or calculate a black hole's event horizon — every tool runs instantly in your browser with no sign-up required.
Observation Tools
ISS Tracker
Real-time ISS orbital tracking.
ObservationMoon Phase
Current lunar phase & age.
ObservationTelescope Magnification
Optics power calculator.
ObservationStellar Parallax
Distance via parallax.
ObservationDawes' Limit
Telescope resolution.
ObservationSidereal Time
Local star time.
ObservationAtmospheric Refraction
Horizon light bending.
Calculation & Conversion Tools
Physics Tools
Black Hole Radius
Event horizon calculator.
PhysicsEscape Velocity
Surface escape speeds.
PhysicsStar Temperature
Wien's Law calculator.
PhysicsRedshift & Hubble
Galaxy distance & z.
PhysicsLight Travel Time
Signal lag to planets.
PhysicsStellar Magnitude
Absolute vs Apparent.
PhysicsSolar Wind Time
Sun-Earth particle travel.
PhysicsStellar Luminosity
Total star power output.
Why Use CosmoToolbox?
CosmoToolbox is a free, browser-based toolkit built for amateur astronomers, students, and anyone curious about the universe. Every tool runs locally on your device, returns instant results, and requires no account, installation, or payment. Whether you are planning an observing session with the moon phase and sidereal time tools or working through an astrophysics problem set, the answer you need is only a click away.
Accuracy and learning go hand in hand here. Each calculator is paired with the exact formula or dataset behind it — from NASA's relative surface gravity values to the SGP4 orbital model used for live ISS tracking — together with plain-English explanations, step-by-step user guides, and FAQs. That makes CosmoToolbox more than a quick calculator: it is a reliable way to understand the science behind every result.