Free Astronomy Calculators and Telescope Utilities

Explore Ontario Telescope’s collection of free astronomy calculators, astrophotography tools, and telescope utilities for visual observers, beginners, and experienced imagers. Calculate autofocuser step size, flat-frame exposure settings, guide scope suitability, double-star resolution and polar alignment tolerance, or check tonight’s observing forecast, upcoming ISS passes, visible rocket launch plumes, which comets are currently observable, and celestial objects visible from your location.

Each free browser-based tool provides practical results to help you plan observing sessions, configure your telescope and camera, improve astrophotography performance, and spend less time guessing under the night sky. No account, subscription, or software download is required.

Built in-house by Ontario Telescope and Accessories.

The code, interface design, artwork, and written explanations of these tools are © 2026 Ontario Telescope and Accessories. All rights reserved.

The astronomy and optics underneath them are not ours, and we claim nothing over them. These tools apply long-published standard work — optical and photometric relations, orbital mechanics, and coordinate transformations — which is free for anyone to use. What is ours is the choice of which methods to apply, how they are assembled, and how the results are explained. Where a tool relies on a particular published source or dataset, it is credited on that tool’s own page.

You are welcome to use them, and to link to any tool from a club newsletter, forum post, or your own site. Please do not copy, rehost, or republish the tools or their code elsewhere. Questions about use? Get in touch.

Results are estimates intended to help you plan an observing session. Sky conditions, equipment, and published launch and orbital data all vary, so treat the output as a guide rather than a guarantee. See our Disclaimer for details.