Chronometer for the Web
A web port of Emerald Chronometer (GitHub), an astronomical watch-face app originally built for iPhone and iPad.
View the project on GitHub · Credits · Privacy · Support · Disclaimer
Your settings are saved in this browser's local storage on this device. Use the Share button to copy a link to a view. See Privacy for more information.
Other Apps
A web port of Emerald Chronometer (GitHub), an astronomical watch-face app originally built for iPhone and iPad.
A web port of Emerald Observatory (GitHub), an astronomical clock app originally built for iPad.
A live data explorer for the astronomy engine shared by Chronometer and Observatory — rise/set times, planetary positions, and calendar and clock values, at any time and location.
Thirty years of solar and lunar eclipses, each with links that open the moment and place of maximum eclipse in Observatory and Chronometer.
General Help Topics
Privacy
Emerald Chronometer for the Web
Overview
Emerald Chronometer for the Web is a fully client-side application. It runs entirely in your browser and does not communicate with any application server for its core functionality.
Data Collection
The app itself does not collect, store, or transmit any personal data to any application server. There are no app-level analytics, tracking pixels, cookies, or telemetry of any kind.
Web Server Logs
When the app is served over HTTP or HTTPS, the hosting provider (SiteGround) records standard web server access logs for each page and resource request. These logs include:
- Your IP address
- The URL requested. The app normally keeps the URL clean; query-string parameters (latitude, longitude, city name, timezone, etc.) appear only when you create or open a shared link
- Timestamp, HTTP status code, referrer, and browser user-agent string
These logs are retained by SiteGround for up to 30 days and are used solely for security monitoring and troubleshooting. They are not analyzed for user tracking purposes.
When running from file:// URLs (a local copy of the app), no
server is involved and no logs are generated.
Map Tile Requests
When you use the location dialog (on pages served via http:// or
https://), the app fetches map tile images from
OpenStreetMap
to display a preview of the selected location.
These requests are standard image fetches and do not include any metadata identifying the tile coordinates as your location — OpenStreetMap sees only which map tile was requested, the same as any map browsing.
Browser Location (Geolocation API)
If you tap "Use device location via browser", the app uses the browser's Geolocation API to obtain your coordinates. This data is processed entirely within the browser — the app never sends it to any application server.
The resolved coordinates are matched against a bundled database of approximately 47,000 cities to display a human-readable location name. This reverse-geolocation lookup happens entirely in the browser — no external geocoding service is contacted.
Local Storage & Sharing
The app saves your settings (location, time, and per-app configuration) in your browser's local storage — on your device only. This data is never sent to any application server, and it persists across visits without any cookies.
You can clear local storage at any time through your browser's settings (typically alongside your browsing history).
When you use the Share button, the app builds a URL that encodes the current view so you can send it to someone else or open it on another device. Opening such a link lets you either use those settings just for that visit or save them as your defaults.
Note: Because shared links carry settings as URL query
parameters, those parameters are visible in your browser history and, when
served over HTTP or HTTPS, in the hosting provider's access logs — but only for
links you deliberately create or open. On file:// pages where
local storage is unavailable, the app falls back to keeping settings in the
URL.
Third-Party Services
- OpenStreetMap (map tiles only, HTTP/HTTPS only) — governed by OSM's privacy policy.
Contact
For questions about this privacy policy, please visit the project on GitHub.
Last updated: May 2026
Support
Emerald Chronometer for the Web
Found a bug? Please report it on the GitHub issues page. Describe what you saw and what you expected, and mention which app and which browser and device you were using, along with the app’s version number (shown at the bottom of the help popup opened by the ℹ︎ button, e.g. “v2.1.8”).
This free web app is maintained by volunteers, so no support or response time is promised — but the developers do read the reports and fix most bugs.
The website itself only serves, as a convenience, files available from the GitHub releases page (see instructions for running the app here).
Disclaimer
Emerald Chronometer for the Web
THIS FREE WEB APP IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
The pages served to your browser are available at the GitHub releases page (see instructions for running the app here).
Mauna Kea (the site of several of the world's largest telescopes) displays a variety of astronomical information.
On Mauna Kea the
outer ring is a 24-hour dial which rotates so that the time of local solar
noon ("local apparent noon"
) is at the top. The Sun indicator shows the local 24-hour time (04:30 in
this example). The outer ring's background is divided into day and night
sections with twilight in between. These regions move according to the season
and the watch's latitude. The straight edges of the yellow semi-circles mark
the exact times of sunrise and sunset (05:53 in the example at left). When
there is no sunrise or sunset (at high latitudes) they disappear behind a
cover. Also on the outer dial is a green triangle indicating the current
UTC
time.
The next ring in is marked with the constellations of the zodiac. It rotates
so that the constellation currently transiting the meridian (i.e., due south
for northern observers) is at the 12 o'clock position on the face (between
Gemini and Taurus in the example at right).
The Sun indicator also shows the position of the Sun in the sky relative to
the zodiac. Another way of saying this is that the zodiac dial rotates once
per
sidereal
day; its numbers represent local apparent sidereal time (approximately, for
times within a few centuries of the present). The Moon indicator shows the
position of the Moon with respect to the zodiac and the Sun (but it is not
related to the time dials).
Note that the positions of the constellations are (approximately) astronomically correct for the present era and do NOT correspond to the "signs" of Western astrology. (The Western division of the sky into constellations is at least 2500 years old; for most of that time astronomy and astrology were the same thing. Though in modern times an astronomer will cringe at being called an astrologer, much of the ancient terminology remains in use in science.)
The small half-dial at 12 o'clock shows the "Equation of Time". Though you
might think from the name that this is the Holy Grail of 21st-century physics,
it is actually just the difference between clock time and
apparent solar time
(or sundial time) for the standard meridian of the local time zone. The arc
spans the actual range of the Equation of Time, from −14.2 to +16.5 minutes.
It varies over the year because the Earth does not move at a constant angular
velocity around the Sun; positive means the sundial is ahead. This was indeed
of critical importance to mariners before the days of electronic navigation.
They could determine their longitude by observing the time of local noon and
comparing that to their chronometers. But that comparison requires adding in
the Equation of Time; without that correction the calculation could be off by
hundreds of miles.
The outer dial, with local solar noon at the top, does not always have 12 o'clock at the top for several reasons. It moves ahead (counterclockwise) for daylight time. It is offset by the Equation of Time (which can be a quarter of an hour either way). And the distance away from the standard meridian of the time zone can result in a shift of more than an hour in some cases.