Astronomy calculators and telescope tools

Calculate telescope magnification from telescope focal length, eyepiece focal length and an explicit Barlow or reducer multiplier.

Divide telescope focal length by clear aperture to calculate the focal ratio as an explicit f-number.

Calculate telescope true field of view from eyepiece apparent field, telescope focal length and eyepiece focal length, with degrees and arcminutes.

Calculate exit pupil from telescope aperture and magnification derived from telescope and eyepiece focal lengths.

Apply the empirical Dawes 116 ÷ aperture-mm relation and convert the resolution estimate to arcseconds, arcminutes and degrees.

Calculate telescope light-gathering power from aperture diameter versus a reference pupil, showing area ratio and aperture area in mm².

Calculate horizontal, vertical and diagonal rectilinear field of view from sensor dimensions and focal length.

Calculate arcseconds per pixel and approximate sensor field from pixel size, focal length and pixel dimensions.

Convert right ascension from hours, minutes and seconds to decimal hours, degrees and arcseconds.

Calculate angular separation between two RA/Dec coordinate pairs, with the answer in degrees, arcminutes and arcseconds.

Convert a Unix timestamp in seconds to Julian Date, Modified Julian Date and elapsed Unix days.

Convert a user-entered distance in kilometres into one-way vacuum light travel time in seconds, minutes and hours.