Sun Clock: An Open-Source, Privacy-First Web App That Tracks the Sun and Moon

Sun Clock is a browser-based 24-hour clock that maps the sun’s position throughout the day, marking sunrise, solar noon, sunset, golden hour, and twilight for the visitor’s location. It layers in lunar data too — the moon’s phase, position, and its rise and set times — and lets users tap or hover over each segment to read exact start and end times. A nice touch of astronomical fidelity: the clock reverses its rotation for Southern Hemisphere users, since the sun tracks anti-clockwise there, echoing the old ‘sunwise’ and ‘widdershins’ terminology that predates mechanical clocks.

On the engineering side, the project has been released as a Progressive Web App, so it can be installed to a device home screen and run offline, and the code now carries an MIT license. Recent updates include dark and auto-color modes, a ticking-seconds option, an annual calendar view, and assorted Safari and display fixes — the incremental polish typical of a maintained open-source side project.

The privacy posture is the detail most likely to resonate with a technical audience: Sun Clock is free, ad-free, and sets no cookies. Location and settings live only in the browser’s local storage and are never transmitted to the server, with the operator collecting aggregate usage stats alone. It’s a small but clean example of building a genuinely useful utility without the tracking scaffolding that usually accompanies location-aware web tools.