Stonehenge Eclipse Calculator
A tool to calculate and predict solar and lunar eclipses based on the theorized methods of Stonehenge’s Aubrey Holes.
Eclipse Prediction Calculator
The date to begin the eclipse prediction simulation.
Number of years to forecast. A 19-year period covers one Metonic cycle.
What is the Stonehenge Eclipse Prediction Method?
The concept to calculate eclipse using stonehenge method stems from the groundbreaking work of astronomer Gerald Hawkins in the 1960s. He proposed that Stonehenge was not merely a temple, but a sophisticated astronomical observatory. His theory, detailed in his book Stonehenge Decoded, suggests that the 56 Aubrey Holes—a ring of pits surrounding the main stone circle—could have been used as a Neolithic “computer” to predict lunar and solar eclipses.
This method is a form of archaeoastronomy that reconstructs how ancient people might have tracked celestial cycles. It is not a modern physics-based calculation but a simulation of a proposed ancient technique. The calculator on this page uses a model inspired by the theories of Hawkins and Sir Fred Hoyle, which involves moving markers representing the Sun, Moon, and lunar nodes around the 56 holes to identify when these bodies would align for an eclipse. This calculator is for anyone interested in ancient astronomy, the history of science, or the mysteries of megalithic structures.
The “Formula” and Logic to Calculate an Eclipse Using the Stonehenge Method
There isn’t a single mathematical formula, but rather a simulation based on astronomical cycles mapped to the 56 Aubrey Holes. The core idea is to track the positions of the Sun, the Moon, and the Lunar Nodes (the two points where the Moon’s orbit crosses the Sun’s path). An eclipse can only occur when a New Moon or Full Moon happens near one of these nodes.
Our calculator simulates this by calculating a “position” (from 1 to 56) for each body for each day in the prediction period:
- Sun’s Position: The Sun completes a circuit of the sky in 365.25 days. Its daily movement is mapped to the 56 holes.
- Moon’s Position: The Moon orbits Earth in about 27.3 days (a sidereal month). Its much faster daily movement is also tracked around the 56 holes.
- Node’s Position: The Lunar Nodes move backward (regress) around the sky over a period of 18.61 years. This slow retrograde motion is arguably the most crucial and difficult cycle to track, and the fact that 56 years is almost exactly three 18.61-year cycles (55.83 years) is a cornerstone of the theory.
An eclipse is predicted when the markers for these three components are in close alignment on the circle of holes.
Variables Table
| Variable | Meaning | Unit / Range | Typical Value |
|---|---|---|---|
| Sidereal Month | Time for the Moon to orbit Earth relative to the stars. | Days | 27.321 |
| Tropical Year | Time for the Sun to return to the same position in the cycle of seasons. | Days | 365.25 |
| Nodal Regression | Time for the Lunar Nodes to make one complete circuit. | Years | 18.61 |
| Aubrey Holes | The number of positions in the predictive system. | Unitless Integer | 56 |
Practical Examples
Example 1: Short-Term Prediction
Let’s say you want to find potential eclipse windows in the near future.
- Inputs:
- Prediction Start Date: Today’s Date
- Prediction Period: 2 years
- Process: The calculator runs the simulation for 730 days. It checks daily for alignments: when the Sun and Moon markers are at the same hole (potential for a solar eclipse) and also near a node marker, or when they are at opposite holes (potential for a lunar eclipse) and near the node markers.
- Results: The table would populate with several dates over the next two years identified as “Eclipse Windows,” providing a rough guide based on this ancient system.
Example 2: A Full Metonic Cycle
The Metonic cycle (~19 years) is a period after which the phases of the Moon recur on the same days of the year. This is a common period used in many ancient calendars.
- Inputs:
- Prediction Start Date: January 1, 2000
- Prediction Period: 19 years
- Process: Using the Aubrey Hole calculator for this longer period demonstrates how the slow drift of the lunar nodes completes a full cycle. The simulation tracks over 6939 days.
- Results: The output would show a long list of eclipse windows spanning nearly two decades, illustrating the recurring patterns that the builders of Stonehenge might have observed and predicted. Comparing these dates to known historical eclipses can be a fascinating exercise, though perfect accuracy is not expected from this simplified model.
How to Use This Stonehenge Eclipse Calculator
Using our tool to calculate eclipse using stonehenge method is straightforward and insightful. Follow these steps:
- Select a Start Date: Use the date picker to choose the first day of your prediction period. By default, it’s set to today.
- Set the Prediction Period: Enter the number of years you want to forecast. For a comprehensive look, try 19 years to cover a full Metonic cycle, or 56 years for a full Aubrey cycle.
- Calculate: Click the “Calculate Predictions” button. The tool will run the day-by-day simulation based on the celestial cycles mapped to the 56 Aubrey Holes.
- Interpret the Results:
- Primary Result: A summary of how many potential eclipse windows were found.
- Intermediate Values: These show the calculated final positions of the Sun, Moon, and Node markers on the 56-hole circle at the very end of your selected period.
- Aubrey Hole Chart: The circular chart visualizes these final marker positions. Hole 1 is at the top (North), with numbers increasing clockwise.
- Results Table: This is the main output, listing the specific dates identified by the model as high-probability eclipse windows. Explore our page on understanding lunar nodes to learn more about why these points are so critical.
Key Factors That Affect Stonehenge Eclipse Predictions
The accuracy and interpretation of predictions from a lunar cycle calculator like this one depend on several key factors, both in the model and in the original theory.
- Initial Marker Positions: The starting alignment of the markers is crucial. The theory assumes an initial calibration based on a known eclipse. Our calculator assumes a simplified starting alignment.
- Cycle Accuracy: The astronomical cycles (27.321 days for the Moon, 18.61 years for the nodes, etc.) are not perfect integers. The model’s accuracy is limited by how it approximates these real-world values.
- Marker Movement Rules: Different researchers, like Fred Hoyle, proposed slightly different rules for how many holes to move the markers and when. This calculator uses a consistent daily movement for simulation purposes.
- Definition of “Alignment”: How close do the markers need to be to trigger a prediction? We use a tolerance of 1-2 holes, as a perfect alignment on a single day is rare in such a model.
- Geographic Location: This model predicts *when* an eclipse might happen globally. It does not and cannot predict if it would have been visible from Stonehenge itself, which requires much more complex calculations.
- The 56-Year Cycle: The relationship between the 56 Aubrey holes and three 18.61-year nodal cycles is the mathematical lynchpin. The small discrepancy (56 vs 55.83 years) would require periodic correction, something ancient astronomers may have done by observing the moon’s actual behavior. Check out our basics of celestial mechanics guide for more info.
Frequently Asked Questions (FAQ)
This calculator is an educational tool that demonstrates a *theory*. It is not a scientifically precise eclipse predictor like those from NASA. It simulates a proposed ancient method and can identify periods of high probability, but it should not be used for actual eclipse viewing plans. The accuracy is surprisingly good for demonstrating the cycles but will not match modern predictions to the day.
The Aubrey Holes are a ring of 56 chalk pits at Stonehenge, dating to the monument’s earliest phase around 3000 BCE. They are named after John Aubrey, who discovered them in the 17th century. While their exact purpose is debated, a leading theory is that they served as an astronomical calculator.
A lunar node is a point in space where the Moon’s orbit, which is tilted by about 5 degrees, intersects with Earth’s orbital plane (the ecliptic). Eclipses can only happen when the Sun and Moon are aligned at or near these nodes.
The number 56 is significant because it relates to several lunar and solar cycles. Most importantly, 56 years is very close to three full cycles of the moon’s nodal regression (3 x 18.61 = 55.83 years). It is also close to five 11.2-year sunspot cycles. This makes it a powerful number for a long-term calendrical computer. Our article on archaeoastronomy explores this further.
Yes. The simulation logic checks for two conditions: the alignment of Sun and Moon at a node (a potential solar eclipse at the New Moon) and the opposition of the Sun and Moon at the nodes (a potential lunar eclipse at the Full Moon). It categorizes the predicted window accordingly.
While we have no written records, the mathematical and astronomical alignments encoded in Stonehenge strongly suggest they did. The theory proposed by Gerald Hawkins and others provides a compelling explanation for the monument’s features that is hard to attribute to pure chance.
No, the number is fixed at 56 as this is central to the entire theory of how Stonehenge worked as an eclipse predictor. Changing it would break the relationship between the structure and the key astronomical cycles.
The Saros Cycle is a period of approximately 18 years, 11 days, 8 hours after which a nearly identical eclipse will occur. The Stonehenge method is one proposed way ancient people might have tracked the underlying cycles (like the nodal regression) that *cause* the Saros cycle. You can learn more on our Saros Cycle page.