Observation Calculators — Astronomy
Planning a night at the eyepiece: field of view, binocular range, Bortle scale sky darkness, and astrophotography exposure. Bortle class sets what is realistically visible, so check it before choosing a target or an exposure.
All Observation Calculators
Calculate maximum exposure time before star trailing from focal length and sensor using the 500 rule.
Calculate the useful range and field of view for binoculars by magnification and aperture.
Estimate your sky darkness on the Bortle scale based on naked-eye limiting magnitude.
Calculate field of view with inputs, formulas, and instant results.
Calculate limiting magnitude with inputs, formulas, and instant results.
Calculate when and where to look for ISS and satellite passes from your location.
Calculate brightness ratio between two stars from their apparent magnitude difference.
Compare telescope value by calculating cost per inch of aperture across models.
Calculate the true field of view for your telescope and eyepiece combination.
Estimate the faintest star your telescope can detect based on aperture diameter.
Calculate telescope magnification with inputs, formulas, and instant results.
About Observation Calculators
Planning a night at the eyepiece: field of view, binocular range, Bortle scale sky darkness, and astrophotography exposure. Bortle class sets what is realistically visible, so check it before choosing a target or an exposure.
Whether you need to solve a one-time problem or verify your own calculations, these free tools cover the most common observation scenarios. All results are computed in your browser — no data is sent to any server.
What You Can Calculate
This section includes 11 tools: Astrophotography Exposure Calculator, Binocular Range Calculator, Bortle Scale Calculator, Field of View Calculator, Limiting Magnitude Calculator, Satellite Visibility Calculator, Star Magnitude Comparison Calculator, Telescope Cost Per Aperture Calculator, and 3 more. Each calculator is free to use with no signup required.