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).
Basel takes its name from the city in Switzerland
, home to
the world's largest watch show. On
Basel, there are 16 hands plus 12 additional indicators.
The primary hands show the
local apparent sidereal time. The hour is read against the inner white dial of 24 numbers (hours of
right ascension, RA), the minutes against the 60 unnumbered tick marks (minutes) on that
dial.
The
precession of the equinoxes
means that the position of the equinox moves with respect to the fixed stars.
But the zero point of right ascension is the vernal equinox. (Equinox, in this
context, means the intersection of the ecliptic plane and the Earth's equator,
named because the apparent path of the Sun crosses that point at the time of
the equinox).
So since Basel's RA dial is fixed, the rings holding the names and
astrological symbols of the constellations of the zodiac rotate slowly to
compensate for the precession. The lines between the constellations indicate
the points where the ecliptic crosses the constellation boundaries (for the
present era). The sidereal hour hand thus indicates which constellation is
currently highest in the sky. (The minute hand has no relation to the
constellations.) In this example, the sidereal time is 22:51 in Aquarius in
the year 2338 CE.
The outer white ring is divided into the months of the year with a hairline at
the beginning of each month and tick marks for every other day; the black tick
marks represent even days of the month, and the spaces between represent odd
days.
It, too, rotates with respect to the RA dial so that the Sun hand indicates
the current date. (May 9 in this example.) But note that the relationship
between the date ring and the zodiac ring is correct only at the position of
the Sun hand, for two reasons: Because the Earth's orbit is elliptical (not an
exact circle), the Sun moves more slowly against the stars at some times
during the year than at others. Also, the Sun's motion is in the ecliptic
plane which is tilted with respect to the reference plane of the RA coordinate
system (the equator). So the Sun does not move at a constant rate around the
RA dial during the year, but speeds up and slows down at intervals. The date
ring rotates so that the current date is always under the Sun, but that means
that other dates are in slightly different spots when the Sun gets there.
There are red hairline indicators over the zodiac ring (fixed at 0, 6, 12, and 18) which mark the positions of the equinoxes and solstices, and a plus sign between Aquarius and Pisces on the zodiac ring which marks the RA position of the vernal equinox in the year 2000. There are four smaller red hairline indicators over the date ring which move slowly to indicate the dates of the equinoxes and solstices. They stay close to the fixed indicators but they don't always line up exactly because as mentioned above the date ring does not match the zodiac ring except exactly at the Sun's position.
The Sun and Moon hands show their positions with respect to the RA dial and
the constellations (and each other). The red
Ω-shaped hands show the positions of the
lunar ascending and descending nodes
(the ascending node indicator has the
Ω rightside-up at 12 o'clock).
When the Sun and Moon coincide and are close to one of the nodes it is
possible that there may be a solar eclipse; when the Sun is close to one node
and the Moon is opposite to it a lunar eclipse may occur.
The eclipse dial at the top center indicates if there is an eclipse happening at the observer's location and time. See Understanding Eclipses for more information about predicting eclipses with the nodal hands and the eclipse dial. For a table of every eclipse from 2011 through 2041 — with links that open each one on Basel — see the Eclipse Table.
Also, note that when the ascending-node hand coincides with the vernal equinox
(at the 12 o'clock position) the Moon will reach extremes in several
dimensions, including north and south declination, northern and southern
azimuths of rise/set points on the horizon, and altitudes crossing the
meridian. See
here
for more detail.
The subdial at 2 o'clock shows
apparent solar time
(sundial time) in 12-hour format. (Note that the Sun hand and the sidereal
hour hand will always coincide when the solar time is 12:00.)
The subdial at 10 o'clock shows UTC in 24-hour format.
The subdial at 6 o'clock shows ordinary clock time with seconds and an AM/PM indicator.
The left window (beneath the UTC subdial) shows the first two digits of the year number (centuries), the right window (beneath the Solar subdial) shows the last two digits.
Finally, just inside the RA dial is a ring which shows the
sidereal times when the Sun and Moon illuminate the sky for this day.
The white region is bounded by sunrise and sunset and thus shows the daytime
hours (in sidereal time). The dark regions represent nighttime with gray when
the Moon is up and black for full night. There are also two tiny hands that
indicate the (sidereal) times of moonrise and moonset. In this example, it is
about an hour before moonrise (as indicated by the sidereal hour hand),
moonset is a bit before 3, and Libra is near the meridian.