Astronomy Calculators
Telescopes, astrophotography and the night sky, worked out in your browser. Free, no sign-up.
Telescopes & optics
Telescope Magnification Calculator
Magnification, exit pupil and true field for any eyepiece.
Open calculatorTelescope Resolution Calculator
Dawes and Rayleigh limits and limiting magnitude.
Open calculatorField of View Calculator
Sky coverage of a camera sensor or an eyepiece.
Open calculatorPixel Scale Calculator
Arcseconds per pixel and sampling for your seeing.
Open calculatorSensor Coverage Calculator
Sensor size and sky area from resolution and pixel size.
Open calculatorAstrophotography
Exposure Time Calculator
Longest untracked exposure by the 500 and NPF rules.
Open calculatorStar Trail Calculator
Trail length in pixels and degrees for any exposure.
Open calculatorMount Tracking Calculator
Tracking rates and drift from polar alignment error.
Open calculatorSNR Estimator
Signal to noise for subs and stacks, and time to target.
Open calculatorCCD Dynamic Range Calculator
Dynamic range in stops and dB from full well and read noise.
Open calculatorSky & observing
Moon Phase Calculator
Phase, illumination and next new and full moon.
Open calculatorSolar Position Calculator
Sun elevation, azimuth, sunrise and sunset for any city.
Open calculatorAir Mass Calculator
Air mass and atmospheric dimming at any altitude.
Open calculatorBortle to SQM Converter
Bortle class, SQM reading and naked-eye limit.
Open calculatorSatellite Visibility Calculator
When a satellite can be seen and how long a pass lasts.
Open calculatorSpace & distance
Light Travel Time Calculator
How long light takes to cross any distance in space.
Open calculatorAngular Size Calculator
How big an object looks from a given distance.
Open calculatorMagnitude Converter
Apparent and absolute magnitude, distance and brightness ratio.
Open calculatorRedshift Distance Converter
Redshift to velocity, distance and lookback time.
Open calculatorOrbital Period Calculator
Kepler's third law: period, orbit size and speed.
Open calculatorAbout these calculators
Each tool shows its working: the formula, what each input means and the rule of thumb behind the advice. They are built for amateur astronomers, astrophotographers, students and teachers, and anyone planning a night under the sky.
The sky tools default to Pakistani cities on Pakistan Standard Time (UTC+5), but any latitude, longitude and time zone works. The northern areas around Gilgit, Hunza and Skardu offer some of the darkest skies in Asia, while Karachi and Lahore sit near the bright end of the Bortle scale.
Need to convert units instead? Try the unit converters or the machine calculators.