Imagine for a moment flying over a landscape. There is a city below you receding to one side, fields coming into view on the other, lots of features to look at as well as flying a plane. You look down and spot a mark in a field, and this is the sort of thing you are looking for; two clear circles and a horseshoe of some sort, just a crop mark but there is something there. So you grab a your camera and snap a couple of photos of it as you pass then carry on looking for more.
More at
https://www.invisibleworks.co.uk/the-henge/
One of our members asked for details of the Clarke excavation of Arminghall Henge - I had a rummage and amazingly this small bit of Antiquity journal from 1935 is Open Access - I love the way it's written:
Link to Antiquity
That is Clarke, J.D.. 1935. Antiquity. Vol IX, p 465-9. including this note: "Norwich representatives of the Electricity Board extended facilities for utilizing their pylon for photographs and showed keen interest..."
The other reference is Clark, G. 1936. The Timber Monument at Arminghall and its Affinities. Proceedings of the Prehistoric Society. Vol II Pt 1 pp 1-51. pp 1-52 which I don't have access to:
Link to Paper
I've tweeted about this here: https://twitter.com/megportal/status/1576202339182350337
Something is not right. This message is just to keep things from messing up down the road