Crops are fading in the drought. And the unusual weather circumstances made the remarkable photos possible, Murphy explains.

“In the late Neolithic, people would have built this henge out of timber,” he says. Imagine massive posts — possibly whole tree trunks — planted in pits and postholes.

“Over time, when the monument fell out of use, the wood all rots away and the holes kind of fill up with organic material,” he said. “But they leave a sort of a fingerprint, or a footprint.” Archaeologists can see it in soil samples. And, in a drought, you can see the impact on crops.

“Those filled-in holes retain a slight amount more moisture than the surrounding soil,” Murphy says. “The crop that is growing out of those features has a very small advantage in terms of additional water and it’s very slightly healthier.”

In normal weather, the difference is undetectable — that’s why Murphy had flown drones overhead before without noticing it. And even in a drought, it’s too subtle to see from the ground.

But combine the dry spell with the aerial view, and suddenly the outline is obvious.

In Ireland, Drought And A Drone Revealed The Outline Of An Ancient Henge : NPR

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