CalAstro — Privacy Policy
CalAstro — Privacy Policy
Last updated: October 28, 2026
CalAstro is a Chrome extension for astronomical calendar conversion, Sun and Moon times, and prayer times. This policy explains what data the extension handles and where it goes.
Summary
- CalAstro has no server, no account, no analytics and no advertising. The publisher receives no data from you.
- All calculations run on your device.
- On first use, CalAstro downloads its astronomical data (about 223 MB, once) from the project's public website. If you look up a date before 1 CE or after 3000 CE, it downloads the data for those years too (about 516 MB, once). Nothing about you is sent.
- The location you choose and your settings are stored only in your browser.
- Apart from these one-time downloads, the extension contacts the network only if you turn on data updates. It then downloads two public scientific files and sends nothing about you.
Data the extension handles
| Data | Purpose | Where it is stored | Shared with |
|---|---|---|---|
| Location you choose (a city from the built-in list, coordinates you type, or your current position when you click "Use my location"), its time zone and elevation | Sun, Moon and prayer times for that place | Chrome extension storage on your device | No one |
| Settings (language, numerals, theme, calendars, calculation methods, saved places) | Remember your preferences | Chrome extension storage on your device | No one |
| Astronomical data downloaded once (JPL ephemeris files) | Sun, Moon and calendar calculations | Extension storage (Cache Storage) on your device | No one |
| Downloaded Earth-orientation and leap-second data (only if updates are on) | Keep time calculations current | Chrome extension storage on your device | No one |
Your location
CalAstro reads your current position only when you click "Use my location". Chrome may ask for your permission first. The position is matched to the nearest place in the extension's built-in list (on your device) to choose a time zone. It is stored only in your browser and is never sent anywhere. You can instead pick a city or type coordinates.
CalAstro has no access to your browsing, tabs, page contents, history, cookies or passwords, and it runs no content scripts.
One-time astronomical data download
The Sun and Moon calculations use NASA JPL's DE442 and DE441
ephemerides. To keep the extension small, these public data files are
not inside the extension package. CalAstro downloads them from the
project's website,
https://reza-ghazi.github.io/calastro/data/ephemeris/,
which is hosted by GitHub Pages:
- when CalAstro is first installed, the data for 1 CE – 3000 CE (about 223 MB);
- the first time you ask for a date before 1 CE or after 3000 CE, the data for 5001 BCE – 1 CE and 3000 – 5000 CE (about 516 MB).
Each file is checked against a SHA-256 checksum packaged with the extension before it is used, and the files are kept on your device across updates, so they are not downloaded again.
These are plain downloads of fixed public files, made without cookies or credentials. As with any web request, GitHub, which hosts the website, sees your IP address and the files requested. Nothing else is sent, and the publisher does not receive this information. Until the download finishes, the Gregorian, Julian and tabular Islamic calendars already work.
Data updates (optional, off until you turn them on)
When you choose Enable automatic updates in Settings, Chrome asks you to allow access to two websites. If you allow it, CalAstro downloads these files, at most about once a week:
https://maia.usno.navy.mil/ser7/finals2000A.all: Earth-orientation parameters published by the IERS (via the U.S. Naval Observatory);https://data.iana.org/time-zones/tzdb/leap-seconds.list: the official leap-second list.
These are plain downloads of public files, made without cookies or credentials. As with any web request, those servers see your IP address. Nothing else is sent. Downloaded files are checked for validity before use, and you can turn updates off at any time; the data packaged with the extension is then used.
Retention and deletion
Your data stays in your browser until you change it. Uninstalling the extension deletes all of its stored data. Settings backups you download are files you control.
Limited use
CalAstro uses data only to provide its calendar, astronomy and prayer-time features. It does not sell or transfer data to third parties, does not use or transfer data for advertising, creditworthiness or any unrelated purpose, and allows no human access to your data. This complies with the Chrome Web Store User Data Policy, including the Limited Use requirements.
Changes
If CalAstro's data practices change, this policy will be updated before the new version is published, and the date above will change.