Digital Stonehenge

 

A self-calibrating solar observatory for a post-astronomy world

The original idea began as a small ML project that could learn time and date from the sun. It did not need ephemeris tables, GPS, or even awareness of where it was placed. The device would simply watch the sky, collect its own sunlight patterns, and build an internal sense of time from scratch. Over time, the concept evolved into something simpler, more robust, and aesthetically more interesting. The final vision became a compact solar observatory, a digital Stonehenge that lives entirely on natural sunlight, a crystal oscillator, and quiet geometry.

At its core, the design uses nothing more than a set of fixed sight lines and a sensitive photodiode. The simplest version discards moving mirrors and scanning steps entirely. Instead, a thick circular lid is drilled with multiple narrow tubes or fitted with thin fiber-optic channels. Each channel points at a specific azimuth and elevation. Most of the day, most of the channels remain dark. Only when the sun crosses the exact line of one of these channels does a burst of light reach the photodiode. A single hit per day is enough to correct internal time drift. Over many days and months, the pattern of which channels fire, and when, builds an implicit map of daily and seasonal sunlight.

The electronics remain minimal, almost primitive. A low-power microcontroller, a photodiode, a simple analog threshold detector or ADC, and a crystal timebase are enough. The device sleeps most of the time. It wakes periodically, samples each fiber channel, and records whether any registered light. When a hit occurs, it saves an event: crystal ticks since last hit, channel ID, intensity. Between hits it simply counts time with its crystal. The top of the device holds a small solar panel to keep the battery charged, a simple compass mark to align it to south at installation, and bubble levels to ensure the geometry stays consistent. The body itself can be built as a circular black box, something between a scientific instrument and an art object, even finished in Japanese lacquer to give it the presence of a crafted talisman.

Although the on-device logic stays intentionally simple, the accumulated data are rich. Months of logs, downloaded weekly or whenever convenient, form a large dataset of sun-angle events. Offline analysis on a laptop or desktop can fit hidden patterns. Without using astronomy tables, the system can discover the length of the local solar day, the date of the solstices, and the repeating structure of the solar year. Daily sun arcs define local solar noon, sunrise, sunset, and day length. Repeated cycles of rising and falling zenith heights gradually reveal the part of the year. With enough data, the system can even infer approximate latitude from the span of angles that the sun crosses. All of these relationships can be learned with simple regression, small sequence models, or even direct curve-fitting. No absolute reference is needed, only sunlight and time increments.

As a doomsday clock, this is a powerful idea. In a world without satellites, time servers, or any external coordination, the device becomes one of the few physical instruments capable of re-establishing a calendar. It tells local solar time based on the last correction from the sun and the drift of its internal crystal. It knows the day in its own solar year, defined by the interval between solstices. It re-learns the length of its year from observation alone. And because e-paper or simple LCD displays can remain off most of the day, the clock only lights up when a human wants to know the time, preserving energy and giving the device a quiet, ancient feel.

Future versions can build on this foundation. A more advanced “model D” version could replace fixed fibers with a tiny mirror, scanning the sky and collecting richer angle-intensity data for more precise models. The same enclosure and power system would still work. A weekly offline workflow can combine logs, train improved models, and upload new coefficients back into the device, letting the system grow smarter over time. In this way the digital Stonehenge becomes both a practical timekeeper and a long-term experimental platform for understanding sunlight, seasons, and autonomous learning.

This concept blends engineering, physics, and craft. It is a functional instrument, a quiet calendar, and a piece of art. And it is something that we can return to, refine, and eventually build into a working prototype.