About CycleCalcs
CycleCalcs is the home for celestial cycles: a free astronomy site built around one idea, that the sky runs on rhythms you can compute, watch, and learn. It began as a few fast calculators and grew into a full observatory bench: a live planetarium Sky Map, a Today in the Sky dashboard, an Eclipse Explorer, a Planet Parade Tracker, a pilotable flythrough of the solar system, a sorted reference of every major astronomical cycle, and a growing library of interactive lessons.
How the site works
Every position, phase, eclipse and rise time on CycleCalcs is computed live in your own browser from the same class of model that serious sky software uses. Nothing is looked up from a fixed table, and the pages send nothing to a server: there are no accounts, no tracking, and the pages work the same for everyone. (The developer API is the one thing that computes on our servers, by design.) Positions are accurate to well under a degree, and the planetary models are reliable for roughly the years 1700 to 2200. The methodology page documents the models, sources and accuracy limits behind every tool.
What we care about
Real astronomy, plainly explained. The site covers what the sky actually does: why the Moon waxes and wanes, why eclipses come in seasons, why planets gather in parades, how the equinoxes drift over 25,920 years. Where a topic has folklore attached, the pages say clearly what is established science, what is history, and what is neither.
No astrology, no forecasts. CycleCalcs computes where things are, not what they mean for your life. Planetary line-ups do not affect events on Earth, and no tool here suggests otherwise. The one numerology calculator is presented for what it is: a classical interpretive tradition with a long history, not science.
Honesty about limits. When a view is illustrative rather than measured (an enlarged planet, an artistic asteroid belt), the page says so. When a value is a long-term average or a contested estimate, the page says that too. Corrections are welcome and acted on.
Free to use, free to share
Every calculator, every page and the API's free tier are free, supported by unobtrusive advertising and clearly disclosed affiliate links: the gear page, plus a small gear card on pages where gear genuinely helps the night, like certified eclipse viewers on an eclipse page. Every card carries its own disclosure. You can also put the sky on your own site with the six free embeddable widgets: moon phase, sunrise and sunset, the next eclipse, a planet parade, what is up tonight, and a cosmic clock. One thing here is not free, and it is the only one: a printable moon calendar computed for your own coordinates, which you can preview for any location before deciding. Selling it is what keeps the rest of this free without asking anyone to sign in.
Privacy in one paragraph
The astronomy runs entirely on your device. Choosing "use my location" or typing a place name is resolved against a place index served with this page, so neither your coordinates nor what you type leaves your browser. Preferences like your theme or saved location live in your own browser's storage, never on our servers. The full detail is in the Privacy Policy.
A note on accuracy
The tools aim to be correct and transparent, but they are provided for general educational and research use. They are not professional financial, investment, legal, or astrological advice. Orbital periods use standard mean values unless a page states otherwise.
Who runs CycleCalcs
CycleCalcs is published by CycleCalcs LLC, a limited liability company formed in the Commonwealth of Virginia, United States of America. The API terms of use and the privacy policy are the binding documents.
Questions, corrections or ideas? Email info@cyclecalcs.com. If you spot a number that looks wrong, please say which page and what you expected; those are the best emails we get.