Stonehenge is a mystery-filled prehistoric monument but one of its mysteries appears to have been solved not because of painstaking scientific research but because of an incident that led to a lightbulb moment.

Experts have long been baffled of Stonehenge's formation. Some archeologists believe that the Neolithic stones of Stonehenge originally formed a perfect circle albeit it is now an incomplete ring. Evidence to support this claim, however, is elusive despite that countless excavations and geophysical surveys have already been conducted.

A dry weather and sheer chance, however, are apparently all it takes to finally settle one of the mysteries of Stonehenge. Stewards usually water the grounds of the site during dry spells to keep the grass healthy but the hose used this year was too short it failed to reach the whole site, in particular a broken part of the circle that eventually dried out and revealed unsightly brown patches.

Site custodian Tim Daw noticed the patches in the incomplete part of the monument's inner stone circle and was actually fretting over them when he realized that the patches were found in the spots where the stones could have been if the monument was a complete circle.

Daw isn't an archeologist but knows the site too well to realize the significance of the parched patches. Archeological features that are buried for a long time affects the growth rate of the grass that grows above them even long after these structures have disappeared. The sight of the parched patches spurred a "lightbulb moment" and prompted Daw to call the experts to evaluate the site.

"A sudden light-bulb moment in my head, and I remembered that the marks were where archaeologists had looked without success for signs that there had been stone holes, and that parch marks can signify them," Daw related. "I called my colleague over and he saw them and realized their possible significance as well."

English Heritage acknowledged that the discovery was indeed significant and may have not occurred if a longer hosepipe has been bought. Archeologist Susan Greaney, Senior Properties Historian at English Heritage, said that although many people think that the entire site has already been excavated and that everything that can be known about the monument has already been discovered, there are still a lot of things that can be learned about the monument with non-excavation methods alone. 

"It's great that people who know the site really well and look at it every day were able to spot these parch marks and recognize them for what they were," Greaney said.