Tools & Calculators
Interactive tools and astronomy calculators to help you plan observations, evaluate equipment, and optimise your astrophotography setup.
Tools
Calculators
Object Visibility & Sky Position
Is This Object Visible Tonight?
Determines whether a celestial object rises high enough to be observed from a given location tonight, from its coordinates and the observer's latitude.
Maximum Altitude of Object
Calculates the highest altitude a celestial object reaches above the horizon from a given latitude, which sets how well it can be observed from that site.
Object Rise and Set Times
Calculates the rise, transit, and set times of a celestial object for a given date and location, from its coordinates and the observer's latitude.
Best Time to Observe Object
Finds the moment a celestial object is highest during the dark hours of a chosen night, when it is best placed for observation from a given location.
Object Altitude vs Time
Plots the altitude of a celestial object across a night, showing when it rises, when it culminates, and when it sinks back toward the horizon.
Airmass Calculator
Calculates the airmass toward an object at a given altitude, a measure of how much atmosphere its light travels through before reaching the observer.
Sidereal Time Calculator
Calculates the local sidereal time for a given longitude and moment, the clock that tracks which celestial coordinates are crossing the meridian.
Hour Angle Calculator
Calculates the hour angle of a celestial object, the angular distance of its position east or west of the meridian at a given time and location.
Telescope & Eyepiece Performance
Telescope Magnification Calculator
Calculates the magnification of a telescope and eyepiece from their focal lengths, and compares it against the telescope's useful magnification range.
Exit Pupil Calculator
Calculates the exit pupil of a telescope and eyepiece, the width of the light beam leaving the eyepiece, which governs image brightness and comfort.
True Field of View Calculator
Calculates the true field of view of a telescope and eyepiece, the actual span of sky visible through them, from their focal lengths and apparent field.
Maximum Useful Magnification
Calculates the highest magnification a telescope can use before the image begins to break down, based on its aperture and the limit set by seeing.
Telescope Resolution Calculator
Calculates the resolving power of a telescope from its aperture, the finest detail and closest double stars it can separate under steady seeing.
Eyepiece Selection Guide
Suggests a set of eyepiece focal lengths that cover a useful range of magnifications for a telescope, from wide low-power views to high-power detail.
Brightness & Visibility
Limiting Magnitude Calculator
Estimates the limiting magnitude of a telescope, the faintest stars it can reveal, from its aperture and the darkness of the observing site.
Surface Brightness Calculator
Calculates the surface brightness of an extended object such as a galaxy or nebula, which predicts how readily it shows against the background sky.
Apparent vs Absolute Magnitude
Converts between apparent and absolute magnitude for a given distance, relating how bright an object looks from Earth to its true luminosity.
Imaging & Astrophotography
Image Scale Calculator
Calculates the image scale of a camera and telescope in arcseconds per pixel, which sets how finely detail is recorded across the sensor.
Field of View (Imaging) Calculator
Calculates the field of view a camera captures through a telescope, from the sensor size and focal length, to help frame a target correctly.
Sampling Calculator
Determines whether a camera and telescope are over-sampled or under-sampled for the local seeing, which affects both sharpness and imaging efficiency.
Pixel Scale vs Seeing
Compares a setup's pixel scale against typical atmospheric seeing, showing whether the camera and telescope are well matched for sharp images.