Observation Tools
Seven hands-on tools for planning and enjoying a night under the stars — follow the ISS in real time, check tonight's moon phase, and get the most out of your telescope optics.
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.
Plan Better Observing Sessions
Successful stargazing starts before dark. Knowing where the International Space Station will pass overhead, how illuminated the moon will be, and when your target stars will cross the local meridian turns a casual glance upward into a productive observing session.
The tools in this category run instantly in your browser: no sign-up, no installation, and every result comes with the formula behind it, so you can trust — and learn from — each calculation. When you are ready for deeper numbers, browse the calculation tools or the physics tools, or view all 20 tools.