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).
Selene (Greek goddess of the Moon) shows the phases of the Moon.
The main black hand indicates the difference between the Moon's ecliptic longitude and the Sun's; this is a representation of the Moon's cycle through the phases. Straight up is new moon (0 age), at right is first quarter (about 7.5 days old), straight down is full moon (about 15 days), left is 3rd (last) quarter (about 22 days old). A complete lunar cycle is about 29.5 days (though it actually varies by several hours from month to month).
Underneath the black hand is a white "Elongation" hand showing the angular separation between the Sun and the Moon in the sky. Note that for most of the time as the Moon increases from New to Full (the right half of the dial), the elongation is very close to the value of “Delta Ecliptic Longitude” (or moon phase) shown by the black hand, and the white elongation hand will be “hiding behind” the black hand. But when the elongation is close to 0 or 180 degrees, and the Moon's ecliptic latitude is not close to zero, the elongation will be different enough for the hand to “peek out”. And during the waning cycle from Full to New (the left side of the dial), the two hands are on opposite sides of the dial and will both be clearly visible, as shown in the images at the top of this page.
When the angular separation is less than about 90 degrees, we calculate it using the positions of the Sun and the Moon as seen from the observer's position (topocentric coordinates), as that is most useful when the objects are close together. When the angular separation is larger than that, we switch to using the positions as seen from the center of the Earth (geocentric coordinates), as that is most useful close to a full moon where there is the possibility of a lunar eclipse (the shadow thrown by the Earth is centered at the Earth center, and doesn't depend on the observer's position).
The outermost dial with the degree markings for the previous two hands is colored alternately dark and light. Each dark or light section represents a 24-hour day, so you can easily count how many days until the next quarter by counting sections from the main black hand to the quarter's indicator. You can also estimate the approximate time of day that quarter will occur by seeing where in its colored section it lies (if the main black line for the quarter is close to the forward part of its colored section, the event will happen late in that day).
These sections are accurate for nearly a full lunar cycle centered around the current time. That is, you can count sections, forward or backward from the main black hand, for 14 days in each direction, which will be just under half a lunar cycle.
The numbers in the quarter icons show the date when that phase occurred or
will occur. The two clockwise from the main hand are in the future, and the
two behind the main hand show dates in the past. The main black hand passes
over the indicator on the date shown. Frequently the dates are in different
calendar months; in example at left for 2020 Feb 1 the previous new moon was
on Jan 24 and the next 1st quarter moon will be Feb 1 later in the day and the
Moon is about 85 degrees east of the Sun.
The small dial at 2 o'clock shows the Moon's ecliptic latitude (which is its angular difference from the Sun in the dimension perpendicular to the longitude). The ticks on the dial represent 1 degree, about twice the apparent diameter of the Moon. When the hand is at the plus side the Moon is north of the Sun. In the example at the left the Moon is about 4.5 degrees south of the ecliptic.
The small dial at 10 o'clock shows the distance from the center of the Earth
to the center of the Moon (in thousands of kilometers). The example at the
left shows a value of about 401,000 km.
At the bottom left is a dial showing the current time, including the day of the month in a window. In the top center are dials showing moonrise and moonset for the current day; a small dot above each is white for AM, black for PM, and red if there is no such event on this day.
At the bottom right is a Moon phase dial like that of Chandra. Just outside the circle of that dial are two additional hands: the red inner one displays the altitude of the Moon from -90 to 90 degrees, and the blue outer one displays the azimuth.
The two thin red triangle hands on the main dial represent the "nodal" points of the Moon's orbit. These are the two points where the Moon's ecliptic latitude is zero, as the Moon cycles above and below the plane defined by the Earth's orbit around the Sun. The position of each hand indicates the delta ecliptic longitude (with respect to the Sun) of that nodal point, so that when the black hand passes over a red nodal point marker, the ecliptic latitude is zero at that time. The nodal markers (unlike the nodal hands on Basel) make a full revolution approximately once per year, as the ecliptic longitude of the Sun makes a similar revolution.
When a nodal marker and the main black hand are both near zero (new moon), a solar eclipse is possible. When both near 180 degrees (full moon), a lunar eclipse is possible.
Lunar eclipses (and solar ones) for thirty years around today are listed in the Eclipse Table.