Twelve independent calculations
Astronomy calculators and telescope tools
Calculate telescope magnification, focal ratio, true field, exit pupil, idealised resolution, light-gathering area, camera field, image scale, coordinate conversions, angular separation, Julian dates and light travel time.
Each page answers one input-driven question with a visible formula. There are no equipment prices, product rankings, hidden catalogue values, observing forecasts or navigation claims.
Calculate telescope magnification from telescope focal length, eyepiece focal length and an explicit Barlow or reducer multiplier.
Open calculator →02Telescope focal ratioDivide telescope focal length by clear aperture to calculate the focal ratio as an explicit f-number.
Open calculator →03Eyepiece true field of viewEstimate true field of view from eyepiece apparent field and telescope magnification, shown in degrees and arcminutes.
Open calculator →04Telescope exit pupilCalculate exit pupil from telescope aperture and magnification derived from telescope and eyepiece focal lengths.
Open calculator →05Dawes limitApply the empirical Dawes 116 ÷ aperture-mm relation and convert the resolution estimate to arcseconds, arcminutes and degrees.
Open calculator →06Light-gathering area ratioCompare circular aperture area with a user-entered reference pupil using the square of the diameter ratio.
Open calculator →07Camera field of viewCalculate horizontal, vertical and diagonal rectilinear field of view from sensor dimensions and focal length.
Open calculator →08Astronomy image scaleCalculate arcseconds per pixel and approximate sensor field from pixel size, focal length and pixel dimensions.
Open calculator →09Right ascension to degreesConvert right ascension from hours, minutes and seconds to decimal hours, degrees and arcseconds.
Open calculator →10Angular separationCalculate great-circle angular separation between two right-ascension and declination coordinate pairs.
Open calculator →11Unix time to Julian dateConvert a Unix timestamp in seconds to Julian Date, Modified Julian Date and elapsed Unix days.
Open calculator →12Light travel timeConvert a user-entered distance in kilometres into one-way vacuum light travel time in seconds, minutes and hours.
Open calculator →Choose by input
Optics, imaging, coordinates or time
Eyepiece and telescope dimensions feed magnification, focal ratio, true-field, exit-pupil and idealised-resolution calculations. Camera sensor data feed field-of-view and image-scale tools. Sky coordinates feed right-ascension conversion and great-circle separation. Numeric time and distance feed Julian-date and light-time conversion.
For dated lunar events, the separate Moon phase calendar keeps official USNO records grouped by year. For local light and twilight, use the city pages from the SkyClock home page.
Planning numbers, not equipment verdicts
These tools expose arithmetic. Real observations also depend on atmosphere, wavelength, optical quality, obstruction, transmission, focus, tracking, calibration and the coordinate reference used. Nothing here selects equipment or replaces independent verification.